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Investigation of ionic and anomalous magnetic behavior in CrSe2 using 8Li β-NMR
J. O. Ticknor, I. Umegaki, R. M. L. McFadden, A. Chatzichristos, D. Fujimoto, V. L. Karner, R. F. Kiefl, S. Kobayashi, C. D. P. Levy, R. Li, G. D. Morris, M. R. Pearson, K. Yoshimura, J. Sugiyama and W. A. MacFarlaneWe have studied a mosaic of 1T-CrSe2 single crystals using β-detected nuclear magnetic resonance of 8Li from 4 to 300 K. We identify two broad resonances that show no evidence of quadrupolar splitting, indicating two magnetically distinct environments for the implanted ion. We observe stretched exponential spin lattice relaxation and a corresponding rate (1/T1) that increases monotonically above 200 K, consistent with the onset of ionic diffusion. A pronounced maximum in 1/T1 is observed at the low temperature magnetic transition near 20 K. Between these limits, 1/T1 exhibits a broad minimum with an anomalous absence of strong features in the vicinity of structural and magnetic transitions between 150 and 200 K. Together, the results suggest 8Li+ site occupation within the van der Waals gap between CrSe2 trilayers. Possible origins of the two environments are discussed.
RSC Adv., 2020,
Local electronic and magnetic properties of the doped topological insulators Bi2Se3:Ca and Bi2Te3:Mn investigated using ion-implanted 8Li β-NMR.
Ryan M. L. McFadden, Aris Chatzichristos, David L. Cortie, Derek Fujimoto, Yew San Hor, Huiwen Ji, Victoria L. Karner, Robert F. Kiefl, C. D. Philip Levy, Ruohong Li, Iain McKenzie, Gerald D. Morris, Matthew R. Pearson, Monika Stachura, Robert J. Cava, and W. Andrew MacFarlaneWe report β−NMR measurements in Bi2Se3:Ca and Bi2Te3:Mn single crystals using 8Li+ implanted to depths on the order of 100 nm. Above ∼ 200 K, spin-lattice relaxation reveals diffusion of 8Li+, with activation energies of ∼ 0.4 eV (∼ 0.2 eV) in Bi2Se3:Ca (Bi2Te3:Mn). At lower temperatures, the NMR properties are those of a heavily doped semiconductor in the metallic limit, with Korringa relaxation and a small, negative, temperature-dependent Knight shift in Bi2Se3:Ca. From this, we make a detailed comparison with the isostructural tetradymite Bi2Te2Se. In the magnetic Bi2Te3:Mn, the effects of the dilute Mn moments predominate, but remarkably the 8Li+ signal is not wiped out through the magnetic transition at 13 K, with a prominent critical peak in the spin-lattice relaxation that is suppressed in a high applied field. This detailed characterization of the 8Li+ NMR response is an important step toward using depth-resolved β−NMR to study the low-energy properties of the chiral topological surface state in the Bi2Ch3 tetradymite topological insulator.
Physical Review B, 102: 235206.
Spin polarized beam for battery materials research: µ±SR and β-NMR
Jun SugiyamaSpin polarized particles exhibiting beta decay, such as muon and 8Li are very useful for detecting internal magnetic fields in solids. Here, I review our attempts to use these spin polarized beams for battery materials research. . .
Hyperfine Interactions 2019 240:1
Ionic and electronic properties of the topological insulator Bi2Te2Se investigated via β-detected nuclear magnetic relaxation and resonance of 8Li
Ryan M. L. McFadden, Aris Chatzichristos, Kim H. Chow, David L. Cortie, Martin H. Dehn, Derek Fujimoto, Masrur D. Hossain, Huiwen Ji, Victoria L. Karner, Robert F. Kiefl, C. D. Philip Levy, Ruohong Li, Iain McKenzie, Gerald D. Morris, Oren Ofer, Matthew R. Pearson, Monika Stachura, Robert J. Cava, and W. Andrew MacFarlaneWe report measurements on the high-temperature ionic and low-temperature electronic properties of the three-dimensional topological insulator Bi2Te2Se using ion-implanted 8Li β-detected nuclear magnetic relaxation and resonance. With implantation energies in the range 5–28 keV, the probes penetrate beyond the expected range of the topological surface state, but are still within 250 nm of the surface. At temperatures above ∼150K, spin-lattice relaxation measurements reveal isolated 8Li+ diffusion with an activation energy EA=0.185(8)eV and attempt frequency τ0−1=8±3×1011s−1 for atomic site-to-site hopping. At lower temperature, we find a linear Korringa-type relaxation mechanism with a field-dependent slope and intercept, which is accompanied by an anomalous field dependence to the resonance shift. We suggest that these may be related to a strong contribution from orbital currents or the magnetic freeze-out of charge carriers in this heavily compensated semiconductor, but that conventional theories are unable to account for the extent of the field dependence. Conventional NMR of the stable host nuclei may help elucidate their origin.
Phys. Rev. B 99, 125201 (2019)
Local metallic and structural properties of the strongly correlated metal LaNiO3 using 8Li β–NMR
Victoria L. Karner, Aris Chatzichristos, David L. Cortie, Martin H. Dehn, Oleksandr Foyevtsov, Kateryna Foyevtsova, Derek Fujimoto, Robert F. Kiefl, C. D. Philip Levy, Ruohong Li, Ryan M. L. McFadden, Gerald D. Morris, Matthew R. Pearson, Monika Stachura, John O. Ticknor, Georg Cristiani, Gennady Logvenov, Friederike Wrobel, Bernhard Keimer, Junjie Zhang, John F. Mitchell, and W. Andrew MacFarlaneWe report β-detected NMR of ion-implanted 8Li in a single crystal and thin film of the strongly correlated metal LaNiO3. Spin-lattice relaxation measurements reveal two distinct local environments, both metallic as evident from T-linear Korringa 1/T1 below 200 K with slopes comparable to other metals. A small approximately temperature-independent Knight shift of ∼ 74 ppm is observed ...
Phys. Rev. B 100, 165109 (2019)
Dynamics of Liquid 1-Ethyl-3-Methylimidazolium Acetate Measured with Implanted-Ion 8Li β-NMR
Derek Fujimoto, Ryan M. L. McFadden, Martin H. Dehn, Yael Petel, Aris Chatzichristos, Lars Hemmingsen, Victoria L. Karner, Robert F. Kiefl, C. D. Philip Levy, Iain McKenzie, Carl A. Michal, Gerald D. Morris, Matthew R. Pearson, Daniel Szunyogh, John O. Ticknor, Monika Stachura, and W. Andrew MacFarlaneWe demonstrate the application of implanted-ion β-detected NMR as a probe of ionic liquid molecular dynamics through the measurement of 8Li spin-lattice relaxation (SLR) and resonance in 1-ethyl-3-methylimidazolium acetate. The motional narrowing of the resonance and the local maxima in the SLR rate, 1/T1, imply sensitivity to subnanosecond Li+ solvation dynamics. From an analysis of 1/T1, we extract an activation energy EA = 74.8(1.5) meV and Vogel–Fulcher–Tammann constant TVFT = 165.8(0.9) K, in agreement with the dynamic viscosity of the bulk solvent. Near the melting point, the lineshape is broad and intense, and the form of the relaxation is nonexponential, reflective of our sensitivity to heterogeneous dynamics near the glass transition. The depth resolution of this technique may later provide a unique means of studying nanoscale phenomena in ionic liquids.
Chem. Mater. 2019, 31, 22, 9346–9353
Bi-Arrhenius Diffusion and Surface Trapping of 8Li+ in Rutile TiO2
A. Chatzichristos, R. M. L. McFadden, M. H. Dehn, S. R. Dunsiger, D. Fujimoto, V. L. Karner, I. McKenzie, G. D. Morris, M. R. Pearson, M. Stachura, J. Sugiyama, J. O. Ticknor, W. A. MacFarlane, and R. F. KieflWe report measurements of the diffusion rate of isolated ion-implanted 8Li+ within ∼120 nm of the surface of oriented single-crystal rutile TiO2 using a radiotracer technique. The α particles from the 8Li decay provide a sensitive monitor of the distance from the surface and how the depth profile of 8Li evolves with time. The main findings are that the implanted Li+ diffuses and traps at the (001) surface. The T dependence of the diffusivity is described by a bi-Arrhenius expression with activation energies of 0.3341(21) eV above 200 K, whereas at lower temperatures it has a much smaller barrier of 0.0313(15) eV. We consider possible origins for the surface trapping, as well the nature of the low-T barrier.
Phys. Rev. Lett. 123, 095901 (2019)
Direct observation of Mg2+ complexes in ionic liquid solutions by 31Mg β-NMR spectroscopy
Daniel Szunyogh, Ryan M. L. McFadden, Victoria L. Karner, Aris Chatzichristos, Thomas Day Goodacre, Martin H. Dehn, Lia Formenti, Derek Fujimoto, Alexander Gottberg, Evan Kallenberg, Ildikó Kálomista, Robert F. Kiefl, Flemming H. Larsen, Jens Lassen, C. D. Philip Levy, Ruohong Li, W. Andrew MacFarlane, Iain McKenzie, Gerald D. Morris, Stavroula Pallada, Matthew R. Pearson, Stephan P. A. Sauer, Paul Schaffer, Peter W. Thulstrup, Lars Hemmingsen, and Monika StachuraNMR spectra of Mg2+ ions in ionic liquids were recorded using a highly sensitive variant of NMR spectroscopy known as β-NMR. The β-NMR spectra of MgCl2 in EMIM-Ac and EMIM-DCA compare favourably with conventional NMR, and exhibit linewidths of ∼3 ppm, allowing for discrimination of species with oxygen and nitrogen coordination.
Dalton Trans., 2018, 47, 14431-14435
Challenge for Detecting the Interface between Electrode and Electrolyte with β-NMR
Jun Sugiyama, Izumi Umegaki, Susumu Shiraki, Taro Hitosugi, Ryan M. L. McFadden, Dongsheng Wang, Victoria Karner, Gerald D. Morris, W. Andrew MacFarlane, and Robert F. KieflIt is widely believed that a space-charge layer (SCL) exists at the vicinity of a boundary between a solid electrolyte layer and electrode layer in an all solid-state Li-ion battery due to the difference of their chemical potentials, although there are no direct experimental evidences. Here, the Li concentration is predicted to decrease drastically in the SCL. In order to clarify whether SCL exists or not, we have attempted to measure the 8Li β-NMR spectrum for a multilayer sample, MgO (50 nm)/Li3PO4 (70 nm)/LiCoO2 (200 nm) as a function of implanted energy of 8Li. The resonance spectrum was fitted by a combination of two Lorentzians and one background signal. Furthermore, the line width of the resonance signal from the Li3PO4 layer is found to become broad towards the boundary with the LiCoO2 layer. This is consistent with the presence of an SCL.
JPS Conf. Proc. 21, 011021 (2018)
Direct measurements of the temperature, depth and processing dependence of phenyl ring dynamics in polystyrene thin films by β-detected NMR
Iain McKenzie, Yu Chai, David L. Cortie, James A. Forrest, Derek Fujimoto, Victoria L. Karner, Robert F. Kiefl, C. D. Philip Levy, W. Andrew MacFarlane, Ryan M. L. McFadden, Gerald D. Morris, Matthew R. Pearsona, and Shipei ZhuThere is indirect evidence that the dynamics of a polymer near a free surface are enhanced compared with the bulk but there are few studies of how dynamics varies with depth. β-Detected nuclear spin relaxation of implanted 8Li+ has been used to directly probe the temperature and depth dependence of the γ-relaxation mode, which is due to phenyl rings undergoing restricted rotation, in thin films of atactic deuterated polystyrene (PS-d8) and determine how the depth dependence of dynamics is affected by sample processing, such as annealing, floating on water and the inclusion of a surfactant, and by the presence of a buried interface. The activation energy for the γ-relaxation process is lower near the free surface. Annealing the PS-d8 films and then immersing in water to mimic the floating procedure used to transfer films had negligible effects on the thickness of the region near the free surface with enhanced mobility. Measurements on a bilayer film indicate enhanced phenyl ring dynamics near the buried interface compared with a single film at the same depth. PS-d8 films annealed with the surfactant sodium dodecyl sulfate (SDS) deposited on the surface show enhanced dynamics in the bulk compared with a pure PS-d8 film and a PS-d8 film where the SDS was washed away. There is less contrast between the surface and bulk in the SDS-treated sample, which could account for the elimination of the Tg confinement effect observed in films containing SDS [Chen and Torkelson, Polymer, 2016, 87, 226].
Soft Matter, 2018,14, 7324-7334
On the Use of 31Mg for β-Detected NMR Studies of Solids
Ryan M. L. McFadden, Aris Chatzichristos, Martin H. Dehn, Derek Fujimoto, Hiroshi Funakubo, Alexander Gottberg, Taro Hitosugi, Victoria L. Karner, Robert F. Kiefl, Mao Kurokawa, Jens Lassen, C. D. Philip Levy, Ruohong Li, Gerald D. Morris, Matthew R. Pearson, Susumu Shiraki, Monika Stachura, Jun Sugiyama, Dániel M. Szunyogh, and W. Andrew MacFarlaneIt has long been desirable to develop a spin-1/2 nucleus as a probe for β-detected NMR studies of solid materials. As a pure magnetic probe, it would greatly compliment our most extensively used nucleus 8Li (spin-2), which is sensitive to both dipolar and quadrupolar interactions. Following the recent successful polarization of spin-1/2 31Mg at TRIUMF, we report here on its use to study solids where host magnesium atoms occupy lattice sites with cubic symmetry — a situation most directly comparable to (stable) 25Mg NMR. We show preliminary results in: rocksalt MgO; spinel MgAl2O4; and antifluorite Mg2Si, which is an interesting semiconducting thermoelectric. Deviations from the results with conventional 25Mg NMR are attributed to the systematics associated with the β-NMR technique. The 31Mg decay chain is found to complicate the extraction of spin–lattice relaxation rates due to a time-dependent background signal introduced by its progeny. The prospect of further use of 31Mg as a β-NMR probe for the study of condensed matter is good.
JPS Conf. Proc. 21, 011047 (2018)
The Spin Relaxation of 8Li+ in Gold at Low Magnetic Field
W. A. MacFarlane, K. H. Chow, M. D. Hossain, V. L. Karner, R. F. Kiefl, R. M. L. McFadden, G. D. Morris, H. Saadaoui, and Z. SalmanHere we report the temperature and applied magnetic field dependence of the spin lattice relaxation of implanted into Au foil in the range 4 to 290 K and 3 to 150 G. Below about 50 G, relaxation due to the dynamic host lattice nuclear spins is important, becoming dominant below 20 G. At 150 G, this process is quenched, and the relaxation is Korringa-like. We report the first measurement of its temperature dependence which shows the characteristic features of the site change around 190 K. At lower field the relaxation is two component above 100 K and exhibits a strong peak at the site change, which we attribute to quadrupolar relaxation of the adjacent Au spins. We discuss the ingredients required for a quantitative theory of the low field relaxation.
JPS Conf. Proc. 21, 011020 (2018)
Developments in µSR and β NMR: Beyond a Muon Lifetime
Robert F. KieflAdvances in the use of μSR and β-NMR are driven by technical developments. New methods were developed which allowed us to learn surprising things about muonium in semiconductors, its electronic structure, its relationship to hydrogen, its ability to diffuse via quantum tunneling, and its metastability. Similarly in the area of high Tc superconductors new capabilities in spectrometer design led to new information on the properties of superconducting vortices and how they interact. The development of low energy β-NMR at TRIUMF and LE-μSR at PSI has made it possible to study electronic and magnetic properties of thin films and interfaces where conventional NMR lacks the required sensitivity. Low energy β-NMR is almost identical to μSR in principle, but the longer lifetime of 8Li allows one to probe the system on a very different time scale. In this sense β-NMR can be viewed as a complement or extension of μSR.
JPS Conf. Proc. 21 011001 (2018)
Beta-Detected NMR of LSAT and YSZ
Victoria L. Karner, Ryan M. L. Mcfadden, Martin H. Dehn, Derek Fujimoto, Aris Chatzichristos, Gerald D. Morris, Matthew R. Pearson, C. D. Philip Levy, Andreas Reisner, Liu H. Tjeng, Robert F. Kiefl, and W. Andrew MacFarlaneUsing 8Li β-NMR we studied two cation substituted solid solutions: yttria-stabilized zirconia (YSZ) and (La,Sr)(Al,Ta)O3 (LSAT). LSAT showed well defined but highly broadened quadrupolar satellites, with a similar pattern to that observed in SrTiO3. In contrast, the resonance in YSZ showed a single, broad peak indicative of a cubic 8Li implantation site. The 8Li spin–lattice relaxation at 6.55 T, for both solid solutions, is very slow; while at 150 G, the relaxation in LSAT becomes faster due to the 27Al nuclear moments similar to Al2O3. For YSZ the low field relaxation rate is also relatively fast possibly due to mobile O2− anions.
JPS Conf. Proc. 21, 011024 (2018)
Beta Detected NMR of LaAlO3
Victoria L. Karner, Ryan M. L. McFadden, Aris Chatzichristos, Gerald D. Morris, Matthew R. Pearson, C. D. Philip Levy, Zaher Salman, David L. Cortie, Robert F. Kiefl, and W. Andrew MacFarlaneUsing 8Li β-NMR we studied the temperature dependence of the spin–lattice relaxation in LaAlO3 in high magnetic field. The relaxation in LAO is composed of two components: a fast-relaxing signal with a small amplitude, and a large amplitude, slow relaxing component. The data was fit using a highly-constrained model which assumes that the temperature dependence of the slow and fast component is the same at all temperatures. The 8Li relaxation suggests a T2 temperature dependence, indicating that the relaxation mechanism could be due to a coupling between the quadrupole moment of 8Li and the soft-mode, low energy phonons in LAO.
JPS Conf. Proc. 21, 011023 (2018)
Exploring the Dynamics of Glasses Using Beta Detected NMR
Victoria L. Karner, Tianyi Liu, Iain McKenzie, Aris Chatzichristos, David L. Cortie, Gerald D. Morris, Robert F. Kiefl, Ryan M. L. McFadden, Zahra Fakhraai, Monika Stachura, and W. Andrew MacFarlaneWe report 8Li spin lattice relaxation in two forms of the molecular glass TPD, one a normal glass and one prepared in an ultrastable configuration. The relaxation is remarkably fast, similar to 8Li relaxation in other organic materials and shows a stretched exponential behavior typical of glasses with a small stretching exponent β = 0.3. At low temperature, there is little or no difference between the two glasses, while above 250 K, the relaxation in the denser ultrastable form is faster. In addition, in this temperature range, the data shows a significant thermal hysteresis.
JPS Conf. Proc. 21, 011022 (2018)
Comparison of 8Li and 9Li Spin Relaxation in SrTiO3 and Pt: A Means to Distinguish Magnetic and Electric Quadrupolar Sources of Relaxation
A. Chatzichristos, R. M. L. McFadden, V. L. Karner, D. L. Cortie, C. D. P. Levy, W. A. MacFarlane, G. D. Morris, M. R. Pearson, Z. Salman, and R. F. KieflWe demonstrate that the ratio of 1/T1 spin–lattice relaxation rates (SLR) of two different isotopes (here 8Li and 9Li) can be used in order to identify the predominant relaxation mechanism within the β-NMR technique. We studied with both isotopes a Pt foil and two samples of single crystal SrTiO3. In Pt, the ratio of the SLR rates was 6.82(29), which is close to but less than the theoretical limit of ∼7.68 for pure magnetic relaxation. In SrTiO3, the weighted averaged SLR ratio of the two samples was 2.7(3), which is close but larger than the theoretical limit of ∼2.14 expected for pure electric quadrupolar relaxation. This indicates that the primary source of relaxation in SrTiO3 is electric quadrupolar in origin and that magnetic effects have a much smaller importance in this material. The low effective asymmetry of 9Li was the dominant cause of uncertainty of the measurements in this study. We propose a system of tagging the beta-decays in coincidence with the alpha decays that take place in two of the three primary decay channels of 9Li as a way of increasing the effective asymmetry and enhance the signal of 9Li β-NMR.
JPS Conf. Proc. 21, 011048 (2018)
Lithium diffusion in spinel Li4Ti5O12 and LiTi2O4 films detected with 8Liβ-NMR
Jun Sugiyama, Izumi Umegaki, Takeshi Uyama, Ryan M. L. McFadden, Susumu Shiraki, Taro Hitosugi, Zaher Salman, Hassan Saadaoui, Gerald D. Morris, W. Andrew MacFarlane, and Robert F. KieflDiffusion of Li+ in (111) oriented thin films of the spinels Li4Ti5O12 and LiTi2O4 has been studied with 8Liβ-detected NMR in the temperature range between 5 and 310 K. In Li4Ti5O12, the spin-lattice relaxation rate (1/T1) versus temperature shows a clear maximum around 100 K (=Tmax) which we attribute to magnetic freezing of dilute Ti3+ local magnetic moments, consistent with the results of magnetization and muon spin relaxation (μ+SR) measurements. The decrease in 1/T1 with temperature above Tmax indicates that Li+ starts to diffuse with a thermal activation energy (Ea) of 0.11(1) eV. In LiTi2O4, on the contrary, as temperature increases from 200 K, 1/T1 increases monotonically up to 310 K. This suggests that Li also starts to diffuse above 200 K with Ea=0.16(2)eV in LiTi2O4. Comparison with conventional Li-NMR on Li4Ti5O12 implies that both β-NMR and μ+SR sense short-range Li motion, i.e., a jump diffusion of Li+ to the nearest neighboring sites.
Phys. Rev. B 96, 094402 (2017)
Towards 31Mg-β-NMR resonance linewidths adequate for applications in magnesium chemistry
M. Stachura, R. M. L. McFadden, A. Chatzichristos, M. H. Dehn, A. Gottberg, L. Hemmingsen, A. Jancso, V. L. Karner, R. F. Kiefl, F. H. Larsen, J. Lassen, C. D. P. Levy, R. Li, W. A. MacFarlane, G. D. Morris, S. Pallada, M. R. Pearson, D. Szunyogh, P. W. Thulstrup and A. VossThe span of most chemical shifts recorded in conventional 25Mg-NMR spectroscopy is ~ 100 ppm. Accordingly, linewidths of ~ 10 ppm or better are desirable to achieve adequate resolution for applications in chemistry. Here we present first high-field 31Mg-β-NMR measurements of 31Mg+ ions implanted into a MgO single crystal carried out at the ISAC facility at TRIUMF. The resonances recorded at 2.5 T and 3.5 T show strong linewidth dependency on the applied RF power, ranging from ~ 419 ppm for the highest RF power down to ~ 48 ppm for the lowest one.
Hyperfine Interact 238, 32 (2017)
β-NMR measurements of molecular-scale lithium-ion dynamics in poly(ethylene oxide)-lithium-salt thin films
Iain McKenzie, David L Cortie, Masashi Harada, Robert F Kiefl, C D Philip Levy, W Andrew MacFarlane, Ryan M L McFadden, Gerald D Morris, Shin-Ichi Ogata, Matthew R Pearson, Jun Sugiyamaβ-detected NMR (β-NMR) has been used to study the molecular-scale dynamics of lithium ions in thin films of poly(ethylene oxide) (PEO) containing either lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) or lithium trifluoroacetate (LiTFA) salts at monomer-to-salt ratios (EO/Li) of 8.3. The results are compared with previous β-NMR measurements on pure PEO and PEO with lithium triflate (LiOTf) at the same loading [McKenzie et al., J. Am. Chem. Soc. 136, 7833 (2014)]. Activated hopping of 8Li+ was observed in all of the films above ∼250 K, with the hopping parameters strongly correlated with the ionicity of the lithium salt rather than the polymer glass transition temperature. The pre-exponential factor increases exponentially with ionicity, while the activation energy for hopping increases approximately linearly, going from 6.3±0.2 kJ mol-1 in PEO:LiTFA to 17.8±0.2 kJ mol-1 in PEO:LiTFSI. The more rapid increase in the pre-exponential factor outweighs the effect of the larger activation energy and results in 8Li+ hopping being fastest in PEO followed by PEO:LiTFSI, PEO:LiOTf, and PEO:LiTFA.
J Chem Phys. 146(24):244903 (2017).
Microscopic Dynamics of Li+ in Rutile TiO2 Revealed by 8Li β-Detected Nuclear Magnetic Resonance
Ryan M. L. McFadden, Terry J. Buck, Aris Chatzichristos, Chia-Chin Chen, Kim H. Chow, David L. Cortie, Martin H. Dehn, Victoria L. Karner, Dimitrios Koumoulis⊥, C. D. Philip Levy, Chilin Li○, Iain McKenzie, Rotraut Merkle, Gerald D. Morris, Matthew R. Pearson, Zaher Salman, Dominik Samuelis, Monika Stachura, Jiyu Xiao, Joachim Maier, Robert F. Kiefl, and W. Andrew MacFarlaneWe report measurements of the dynamics of isolated 8Li+ in single crystal rutile TiO2 using β-detected nuclear magnetic resonance. From spin–lattice relaxation and motional narrowing, we find two sets of thermally activated dynamics: one below 100 K and one at higher temperatures. At low temperature, the activation barrier is 26.8(6) meV with prefactor 1.23(5) × 1010 s–1. We suggest this is unrelated to Li+ motion and rather is a consequence of electron polarons in the vicinity of the implanted 8Li+ that are known to become mobile in this temperature range. Above 100 K, Li+ undergoes long-range diffusion as an isolated uncomplexed cation, characterized by an activation energy and prefactor of 0.32(2) eV and 1.0(5) × 1016 s–1, respectively, in agreement with macroscopic diffusion measurements. These results in the dilute limit from a microscopic probe indicate that Li+ concentration does not limit the diffusivity even up to high concentrations but that some key ingredient is missing in the calculations of the migration barrier. The anomalous prefactors provide further insight into both Li+ and polaron motion.
Chem. Mater. 2017, 29, 23, 10187–10197
β-NMR Investigation of the Depth-Dependent Magnetic Properties of an Antiferromagnetic Surface
D. L. Cortie, T. Buck, M. H. Dehn, V. L. Karner, R. F. Kiefl, C. D. P. Levy, R. M. L. McFadden, G. D. Morris, I. McKenzie, M. R. Pearson, X. L. Wang, and W. A. MacFarlaneBy measuring the prototypical antiferromagnet α−Fe2O3, we show that it is possible to determine the static spin orientation and dynamic spin correlations within nanometers from an antiferromagnetic surface using the nuclear spin polarization of implanted 8Li+ ions detected with β-NMR. Remarkably, the first-order Morin spin reorientation in single crystal α−Fe2O3 occurs at the same temperature at all depths between 1 and 100 nm from the (110) surface; however, the implanted nuclear spin experiences an increased 1/T1 relaxation rate at shallow depths revealing soft-surface magnons. The surface-localized dynamics decay towards the bulk with a characteristic length of ε=11 nm, closely matching the finite-size thresholds of hematite nanostructures.
Phys. Rev. Lett. 116, 106103 (2016)
Enhanced high-frequency molecular dynamics in the near-surface region of polystyrene thin films observed with β-NMR
Iain McKenzie, Chad R. Daley, Robert F. Kiefl, C. D. Philip Levy, W. Andrew MacFarlane, Gerald D. Morris, Matthew R. Pearson, Dong Wang, and James A. Forrestcβ-detected nuclear spin relaxation of 8Li+ has been used to probe the depth dependence of molecular dynamics in high- and low-molecular-weight deuterated polystyrene. The average nuclear spin–lattice relaxation rate, 1/Tavg1, is a measure of the spectral density of the polymer motion at the Larmor frequency (41 MHz at 6.55 T). In both samples, 1/Tavg1 is depth independent below ∼200 K but above this temperature it decreases approximately exponentially with distance from the free surface, returning to bulk behavior for depths greater than ∼10 nm. This is direct evidence for a region near the free surface with enhanced molecular dynamics compared with the bulk. The effective thickness of the surface region increases with increasing temperature and is finite even above the glass transition. These results present challenges for the current understanding of dynamics near the surface of polymer glasses.
Soft Matter, 2015,11, 1755-1761
β-detected NMR spin relaxation in a thin film heterostructure of ferromagnetic EuO
W. A. MacFarlane, Q. Song, N. J. C. Ingle, K. H. Chow, M. Egilmez, I. Fan, M. D. Hossain, R. F. Kiefl, C. D. P. Levy, G. D. Morris, T. J. Parolin, M. R. Pearson, H. Saadaoui, Z. Salman, and D. WangWe present β-detected NMR measurements of the spin-lattice relaxation of 8Li+ implanted into an epitaxial heterostructure based on a 100 nm thick film of ferromagnetic (FM) EuO as a function of temperature through its FM transition. In the FM state, the spin-lattice relaxation rate follows the same temperature dependence, determined by magnon scattering mechanisms, observed in the bulk by 153Eu NMR, but above 40 K, the signal is wiped out. We also find that 8Li+ stopped in material adjacent to the magnetic layer exhibits spin relaxation related to the critical slowing of the Eu spins. A particularly strong relaxation in the Au overlayer suggests an unusual strong nonlocal coupling mechanism to 8Li in the metal.
Phys. Rev. B 92, 064409 (2015)
Implanted-ion βNMR: A new probe for nanoscience
W. A. MacFarlaneNMR detected by radioactive beta decay, β-NMR, is undergoing a renaissance largely due to the availability of high intensity low energy beams of the most common probe ion, 8Li+, and dedicated facilities for materials research. The radioactive detection scheme, combined with the low energy ion beam, enable depth resolved NMR measurements in crystals, thin films and multilayers on depth scales of 2–200 nm. After a brief historical introduction, technical aspects of implanted-ion β-NMR are presented, followed by a review of recent applications to a wide range of solids.
Solid State Nuclear Magnetic Resonance 78-69: 1-12 (2015)
Nanoscale β-nuclear magnetic resonance depth imaging of topological insulators
Dimitrios Koumoulis, Gerald D Morris, Liang He, Xufeng Kou, Danny King, Dong Wang, Masrur D Hossain, Kang L Wang, Gregory A Fiete, Mercouri G Kanatzidis, Louis-S BouchardConsiderable evidence suggests that variations in the properties of topological insulators (TIs) at the nanoscale and at interfaces can strongly affect the physics of topological materials. Therefore, a detailed understanding of surface states and interface coupling is crucial to the search for and applications of new topological phases of matter. Currently, no methods can provide depth profiling near surfaces or at interfaces of topologically inequivalent materials. Such a method could advance the study of interactions. Herein, we present a noninvasive depth-profiling technique based on β-detected NMR (β-NMR) spectroscopy of radioactive 8Li+ ions that can provide “one-dimensional imaging” in films of fixed thickness and generates nanoscale views of the electronic wavefunctions and magnetic order at topological surfaces and interfaces. By mapping the 8Li nuclear resonance near the surface and 10-nm deep into the bulk of pure and Cr-doped bismuth antimony telluride films, we provide signatures related to the TI properties and their topological nontrivial characteristics that affect the electron–nuclear hyperfine field, the metallic shift, and magnetic order. These nanoscale variations in β-NMR parameters reflect the unconventional properties of the topological materials under study, and understanding the role of heterogeneities is expected to lead to the discovery of novel phenomena involving quantum materials.
Proc Natl Acad Sci USA. 2015 Jul 14; 112(28):E3645-50.
Spin fluctuations in the exotic metallic state of Sr2RuO4 studied with β-NMR
D. L. Cortie, T. Buck, M. H. Dehn, R. F. Kiefl, C. D. P. Levy, R. M. L. McFadden, G. D. Morris, M. R. Pearson, Z. Salman, Y. Maeno, and W. A. MacFarlaneA β-NMR study was performed on a Sr2RuO4 crystal in the metallic state using a beam of spin-polarized 8Li+ implanted at a mean depth of 90 nm. The 8Li+ spin-lattice relaxation rate is strongly influenced by the onset of incommensurate spin fluctuations. The nuclear relaxation rate can be explained using previously published bulk 17O NMR and inelastic neutron spectroscopy measurements of the dynamic magnetic susceptibility to model the hyperfine coupling. A well-resolved quadrupolar-split NMR for 8Li+ implies a static stopping position in an interstitial site. The 8Li+ Knight shift is highly sensitive to the anisotropic static susceptibility.
Phys. Rev. B 91, 241113(R) (2015)
8Li β-NMR study of epitaxial LixCoO2 films
J Sugiyama, M Harada, H Oki, S Shiraki, T Hitosugi, O Ofer, Z Salman, Q Song, D Wang, H Saadaoui, G D Morris, K H Chow, W A MacFarlane, and R F KieflIn order to investigate the diffusive motion of Li+ in a thin film electrode material for Li-ion batteries, we have measured β-NMR spectra of 8Li+ ions implanted into epitaxial films of Li0.7CoO2 and LiCoO2 in the temperature range between 10 and 310 K. Below 100 K, the spin-lattice relaxation rate (1/T1) in the Li0.7CoO2 film increased with decreasing temperature, indicating the appearance and evolution of localized magnetic moments, as observed with µSR. As temperature is increased from 100 K, 1/T1 starts to increase above ~200 K, where both Li-NMR and µSR also sensed an increase in 1/T1 due to Li-diffusion. Interestingly, such diffusive behavior was found to depend on the implantation energy, possibly because the surface of the film is decomposed due to chemical instability of the Li0.7CoO2 phase in air. Such diffusive behavior was not observed for the LiCoO2 film up to 310 K.
J. Phys. Conference Series 551: 012009 (2014)
A Brief Survey of β-Detected NMR of Implanted 8Li+ in Organic Polymers
McGee, F. H.; McKenzie, I.; Buck, T.; Daley, C. R.; Forrest, J. A.; Harada, M.; Kiefl, R. F.; Levy, C. D. P.; Morris, G. D.; Pearson, M. R.; Sugiyama, J.; Wang, D.; MacFarlane, W. A.Unlike the positive muon, we expect the chemistry of the implanted 8Li+β-NMR probe in organic polymers to be simply that of the monovalent ion, but almost nothing is known about the NMR of isolated Li+ in this context. Here, we present a brief survey of 8Li+β-NMR in a variety of insulating polymers at high magnetic field, including polyimide, PET, polycarbonate, polystyrene and polyethylene oxide. In all cases, we find a large-amplitude, broad Lorentzian resonance near the Larmor frequency, consistent with the expected diamagnetic charge state. We also find remarkably fast spin-lattice relaxation rates 1/T1. There is very little dependence of either linewidth or 1/T1 on the proton density, the main source of nuclear dipolar magnetic fields, leading us to conclude the main contribution to both broadening and spin relaxation at room temperature is quadrupolar in origin. This behaviour is very different from crystalline insulators such as MgO and Al2O3, and suggests that 8Li+β-NMR will be an important probe of polymer dynamics. Additionally, we note dramatically different behaviour of one sample above its glass transition, motivating the construction of a high temperature spectrometer to enable further exploration at elevated temperature.
Journal of Physics: Conference Series, Volume 551, Issue 1, article id. 012039 (2014).
β-NMR of 8Li+ in rutile TiO2
R M L McFadden, D L Cortie, D J Arseneau, T J Buck, C-C Chen, M H Dehn, S R Dunsiger, R F Kiefl, C D P Levy, C Li, G D Morris, M R Pearson, D Samuelis, J Xiao, J Maier, and W A MacFarlaneWe report preliminary low-energy β-NMR measurements of 8Li+ implanted in single crystal rutile TiO2 at an applied field of 6.55 T and 300 K. We observe a broad 12 kHz wide quadrupole split resonance with unresolved features and a sharp component at the Larmor frequency. The line broadening may be caused by overlapping multi-quantum transitions or motion of 8Li+ on the scale of its lifetime (1.21 s). We also find spin-lattice relaxation that is relatively fast compared to other wide band gap insulators. The origin of this fast relaxation is also likely quadrupolar and may be due to anisotropic 8Li+ diffusion.
J. Phys.: Conf. Ser. 551 012032 (2014)
8Li+ β-NMR in the Cubic Insulator MgO
W A MacFarlane, T J Parolin, D L Cortie, K H Chow, M D Hossain, R F Kiefl, C D P Levy, R M L McFadden, G D Morris, M R Pearson, H Saadaoui, Z Salman, Q Song, and D WangWe present extensive high magnetic field β-NMR measurements of 8Li+ implanted in single crystals of MgO. The narrow resonance, consistent with a cubic 8Li+ site, likely the tetrahedral interstitital, is used routinely as a reference for shift measurements. We show the intrinsic linewidth is on the order of 200 Hz, allowing a frequency determination to an accuracy of a few Hz. We find no implantation energy dependence of the resonance within a few ppm, but there is evidence of slow spin dynamics in hole-burning measurements. The spin lattice relaxation is slow. The temperature dependence reveals interesting changes at low temperature whose origin remains uncertain.
J. Phys.: Conf. Ser. 551 012033 (2014)
β-detected nuclear quadrupole resonance and relaxation of 8Li+ in sapphire
Z Salman, K H Chow, M D Hossain, R F Kiefl, C D P Levy, T J Parolin, M R Pearson, H Saadaoui, D Wang, and W A MacFarlaneWe report detailed behaviour of low energy 8Li implanted near the surface of α-Al2O3 single crystal, as revealed by beta-detected NQR of 8Li. We find that the implanted 8Li occupies at least two sites with non-cubic symmetry in the Al2O3 lattice. In both sites the 8Li experiences axially symmetric electric field gradient, with the main principal axis along the c-crystallographic direction. The temperature and field dependence of the spin lattice relaxation of 8Li in α-Al2O3, indicate that the 8Li diffusion is negligible on the scale of its lifetime, 1.21 s.
J. Phys.: Conf. Ser. 551 012034 (2014)
The Initial State of Optically Polarized 8Li+ from the β-NMR in Bismuth
W A MacFarlane, C D P Levy, M R Pearson, T Buck, K H Chow, A N Hariwal, R F Kiefl, F H McGee, G D Morris, and D WangUnlike the positive muon, β-NMR probe nuclei must be actively polarized. At the TRIUMF ISAC facility this is accomplished by in-flight collinear optical pumping with resonant circularly polarized laser light. This reliably produces a high degree of polarization, but the detailed state populations in the beam emerging from the optical polarizer are not well known. These populations are significant as they represent the initial state of the ensemble of probe spins implanted in a β-NMR experiment. Here we use the well-resolved quadrupolar split spectrum of 8Li+ in a high purity single crystal of bismuth to extract the sublevel populations under typical polarizer operating conditions, accounting for the spin relaxation in this semimetal.
J. Phys.: Conf. Ser. 551 012059 (2014)
β-NMR Study of a buried Mn δ-doped layer in a silicon host
D Cortie, T Buck, R M L McFadden, J Xiao, C D P Levy, M Dehn, M Pearson, G D Morris, S R Dunsiger, R F Kiefl, F J Rueß, A Fuhrer, and W A MacFarlaneLow temperature growth methods were used to encapsulate a buried Mn δ-doping layer into a silicon host. A β-NMR investigation was performed of the magnetic properties in the temperature range 10 – 300 K using spin-polarized 8Li+. A depth-dependent broadening and shift of the NMR resonance was detected that is consistent with internal fields distributed at depths of 10 – 30 nm beneath the surface. At low temperatures, a negative relative shift occurred and the resonance was significantly broadened. At 300 K the line-shape could be described by a single Gaussian line, however, at 10 K the line is best approximated by a two component Lorentzian shape consisting of a broad and narrow component as anticipated for a diluted magnetic alloy. The overall magnitude of the resonance shift at both temperatures is small suggesting a weak interaction between the 8Li+ and the magnetic Mn environment.
J. Phys.: Conf. Ser. 551 012023 (2014)
β-Detected NMR Search for Magnetic Phase Separation in Epitaxial GaAs:Mn
Q. Song, K.H. Chow, R.I. Miller, I. Fan, M.D. Hossain, R.F. Kiefl, G.D. Morris, S.R. Kreitzman, C.D.P. Levy, T.J. Parolin, M.R. Pearson, Z. Salman, H. Saadaoui, M. Smadella, D. Wang, K.M. Yu, X. Liu, J.K. Furdyna, and W.A.MacFarlaneTo test for the microscopic magnetic phase separation in the dilute magnetic semiconductor Ga1−xMnxAs suggested by low energy muon spin rotation measurements, we present a detailed analysis of the amplitudes of the 8Li β-detected nuclear magnetic resonance in an epitaxially grown thin film of x = 5.4% Mn doped GaAs on a semi-insulating GaAs substrate with magnetic transition temperature TC =72 K. The spectrum at 100 K corresponds to 73% of the full room temperature amplitude, and at 60 K to about 62%. The 11% loss of signal through the magnetic tran-sition is much smaller than that ∼ 50% found by low energy μSR, and may be entirely due to an amplitude change intrinsic to GaAs. This lack of evidence for phase separation is, however, consistent with the full volume fraction magnetism found by a second low energy μSR measurement on a different sample using weak transverse field.
Physics Procedia 30, 2012, 174-177
β-NMR Measurements of Lithium Ion Transport in Thin Films of Pure and Lithium-Salt-Doped Poly(ethylene oxide)
I. McKenzie, M. Harada, R. F. Kiefl, C. D. P. Levy, W. A. MacFarlane, G. D. Morris, S.-I. Ogata, M. R. Pearson, and J. Sugiyama
β-Detected nuclear spin relaxation of 8Li+ has been used to study the microscopic diffusion of lithium ions in thin films of poly(ethylene oxide) (PEO), where the implanted lithium ions are present in extremely low concentration, and PEO with 30 wt % LiCF3SO3 over a wide range of temperatures both above and below the glass transition temperature. Recent measurements by Do et al. [Phys. Rev. Lett. 2013, 111, 018301] found that the temperature dependence of the Li+ conductivity was identical to that of the dielectric α relaxation and was well described by the Vogel-Fulcher-Tammann relation, implying the α relaxation dominates the Li+ transport process. In contrast, we find the hopping of Li+ in both samples in the high temperature viscoelastic phase follows an Arrhenius law and depends significantly on the salt content. We propose that the hopping of Li+ between cages involves motion of the polymer but that it is only for long-range diffusion where the α relaxation plays an important role.
J. Am. Chem. Soc., 2014, 136 (22), pp 7833-7836
Finite-size effects in the nuclear magnetic resonance of epitaxial palladium thin films
W. A. MacFarlane, T. J. Parolin, T. I. Larkin, G. Richter, K. H. Chow, M. D. Hossain, R. F. Kiefl, C. D. P. Levy, G. D. Morris, O. Ofer, M. R. Pearson, H. Saadaoui, Q. Song, and D. WangWe have measured the NMR of 8Li+ implanted in a set of thin epitaxial films of Pd. We find a large, negative, strongly temperature-dependent Knight shift K consistent with previous measurements on polycrystalline films. The temperature dependence of the shift exhibits a characteristic deviation from the susceptibility Χ(T). In particular, at low temperature,
Phys. Rev. B
Nature of Weak Magnetism in SrTiO3/LaAlO3 Multilayers
Z. Salman, Oren Ofer, M. Radovic, H. Hao, M. Ben Shalom, K. H. Chow, Y. Dagan, M. D. Hossain, C. D. P. Levy, W. A. MacFarlane, G. M. Morris, L. Patthey, M. R. Pearson, H. Saadaoui, T. Schmitt, D. Wang, and R. F. KieflWe report the observation of weak magnetism in superlattices of LaAlO3/SrTiO3 using β-detected nuclear magnetic resonance. The spin lattice relaxation rate of 8Li in superlattices with a spacer layers of 8 and 6 unit cells of LaAlO3 exhibits a strong peak near ∼35 K, whereas no such peak is observed in a superlattice with spacer layer thickness of 3 unit cells. We attribute the observed temperature dependence to slowing down of weakly coupled electronic moments at the LaAlO3/SrTiO3 interface. These results show that the magnetism at the interface depends strongly on the thickness of the spacer layer, and that a minimal thickness of ∼4–6 unit cells is required for the appearance of magnetism. A simple model is used to determine that the observed relaxation is due to small fluctuating moments (∼0.002μB) in the two samples with a larger LaAlO3 spacer thickness.
Phys. Rev. Lett. 109, 257207 (2012)
β-NMR study of isolated 8Li+ in the enhanced paramagnet platinum
Oren Ofer, K. H. Chow, I. Fan, M. Egilmez, T. J. Parolin, M. D. Hossain, J. Jung, Z. Salman, R. F. Kiefl, C. D. P. Levy, G. D. Morris, M. R. Pearson, H. Saadaoui, Q. Song, D. Wang, and W. A. MacFarlaneWe report β-detected nuclear magnetic resonance (β-NMR) measurements of 8Li+ implanted into high purity Pt. The frequency of the 8Li β-NMR resonance and the spin-lattice relaxation rates 1/T1 were measured at temperatures ranging from 3 to 300 K. Remarkably, both the spin-lattice relaxation rate and the Knight shift K depend linearly on temperature T although the bulk susceptibility does not. K is found to scale with the Curie-Weiss dependence of the Pt susceptibility extrapolated to low temperatures. This is attributed to a defect response of the enhanced paramagnetism of Pt, i.e., the presence of the interstitial Li+ locally relieves the tendency for the Curie-Weiss susceptibility to saturate at low T. We propose that the low temperature saturation in χ of Pt may be related to an interband coupling between the s and d bands that is disrupted locally by the presence of the Li+.
Phys. Rev. B 86, 064419 (2012)
Slow order-parameter fluctuations in superconducting Pb and Ag/Nb films observed using β-detected nuclear magnetic resonance
We report β-NMR investigations of polarized 8Li implanted in thin Pb and Ag/Nb films. At the critical superconducting temperature, we observe a singular peak in the spin relaxation rate in small longitudinal magnetic fields, which is attributed to unexpected slow fluctuations in the superconducting order parameter. The peak is several orders of magnitude larger than the prediction based on the enhancement of the dynamic electron spin susceptibility by superconducting fluctuations. The observed peak in 1/T1 is rapidly suppressed in a small magnetic field, indicating that it is due to remarkably slow diamagnetic fluctuations which are undetectable with conventional NMR.
Detection and decoherence of level-crossing resonances of 8Li in Cu
Level-crossing resonances are observed for spin-polarized 8Li in copper at 200 K. The positions of the resonances as a function of magnetic field and crystal orientation are a precise measure of the induced quadrupolar interaction on the nearest-neighbor Cu spins and provide unambiguous evidence that 8Li occupies a substitutional site. The resonances are detected as enhancements in the 8Li spin relaxation rate and are much broader than predicted from a static spin Hamiltonian. A strong collision model is used to extract a decoherence time as a result of the dipolar coupling of the 8Li-Cu subsystem to the surrounding nuclear spin bath.
β-detected NMR of Li in Ga1-xMnxAs
The magnetic properties of a 180-nm-thick epitaxial film of the dilute magnetic semiconductor Ga1−xMnxAs with x=0.054 are investigated using beta-detected NMR of low-energy implanted 8Li+. There is a broad distribution of local magnetic fields in the Ga1−xMnxAs layer, reflecting the magnetic inhomogeneity of the system. The resonance (representing the local magnetic field distribution) is followed as a function of temperature through the ferromagnetic transition. The average hyperfine field at the 8Li+ nucleus is measured to be positive and on the order of 150 G at low temperature, implying a negative hyperfine coupling of the 8Li+ to the delocalized holes and suggesting that the holes are better described by an Mn–derived impurity band. The spin–lattice relaxation of 8Li+ shows a remarkably weak feature at the phase transition and no Korringa behavior despite metallic conductivity. No evidence is found of the microscopic magnetic phase separation that has been suggested by some low-energy muon spin-rotation measurements.
Depth dependence of the structural phase transition of SrTiO3 studied with β-NMR and grazing incidence x-ray diffraction
Abstract
We present an investigation of the near-surface tetragonal phase transition in SrTiO3, using the complementary techniques of beta-detected nuclear magnetic resonance and grazing-incidence X-ray diffraction. The results show a clear depth dependence of the phase transition on scales of a few microns. The measurements support a model in which there are tetragonal domains forming in the sample at temperatures much higher than the bulk phase transition temperature. Moreover, we find that these domains tend to form at higher temperatures preferentially near the free surface of the crystal. The details of the tetragonal domain formation and their depth/lateral dependencies are discussed.Phys. Rev. B 83, 224112 (2011)
Search for broken time-reversal
symmetry near the surface of superconducting YBa2Cu3O7−δ
films using β-detected nuclear magnetic resonance
Abstract
Weak spontaneous magnetic fields are observed near the surface of YBa2Cu3O7-δ films using β-detected nuclear magnetic resonance. Below Tc, the magnetic field distribution in a silver film evaporated onto the superconductor shows additional line broadening, indicating the appearance of small disordered magnetic fields. The line broadening increases linearly with a weak external magnetic field applied parallel to the surface, and is depth independent up to 45 nm from the Ag/YBa2Cu3O7-δ interface. The magnitude of the line broadening extrapolated to zero applied field is less than 0.2 G, and is close to nuclear dipolar broadening in the Ag. This indicates that any fields due to broken time-reversal symmetry are less than 0.2 G.Phys. Rev. B 83, 054504 (2011)
ArXiv link
Nuclear magnetic resonance study of
Li implanted in a thin film of niobium
Abstract
We report results of beta-detected NMR of 8Li+ implanted in Nb at high magnetic field. We identify two distinct sites for 8Li in the body-centered lattice. At low temperature, the site is characterized by a well-defined quadrupolar splitting. At about 50 K this site becomes unstable. Close to room temperature, Li occupies the cubic substitutional site. Spin-lattice relaxation measurements are consistent with a site-dependent coupling to the Nb conduction electrons and suggest that the site change proceeds in two steps. We report Knight shifts for the two well-defined sites and perform a Korringa analysis.Phys. Rev. B 80, 174109 (2009)
Vortex lattice disorder in YBa2Cu3O7−δ
probed using β-NMR
Abstract
β-detected NMR (β-NMR) has been used to study vortex lattice disorder near the surface of the high-TC superconductor YBa2Cu3O7−δ (YBCO). The magnetic-field distribution from the vortex lattice was detected by implanting a low-energy beam of highly polarized 8Li+ into a thin overlayer of silver on optimally doped, twinned, and detwinned YBCO samples. The resonance in Ag broadens significantly below the transition temperature TC as expected from the emerging field lines of the vortex lattice in YBCO. However, the lineshape is more symmetric and the dependence on the applied magnetic field is much weaker than expected from an ideal vortex lattice, indicating that the vortex density varies across the face of the sample, likely due to pinning at twin boundaries. At low temperatures the broadening from such disorder does not scale with the superfluid density.Phys. Rev. B 80, 224503 (2009)
High resolution β-NMR study of Li
implanted in gold
T. J. Parolin, Z. Salman, K. H. Chow, Q. Song, J. Valiani, H. Saadaoui, A. O’Halloran, M. D. Hossain, T. A. Keeler, R. F. Kiefl, S. R. Kreitzman, C. D. P. Levy, R. I. Miller, G. D. Morris, M. R. Pearson, M. Smadella, D. Wang, M. Xu, and W. A. MacFarlane
Abstract
Phys. Rev. B 77, 214107 (2008)
Proximal Magnetometry in Thin Films
using β-NMR
M. Xu, M.D. Hossain, H. Saadaoui, T.J. Parolin, K.H. Chow, T.A. Keeler, R.F. Kiefl, G.D. Morris, Z. Salman, Q. Song, D. Wang, W.A. MacFarlane
Abstract
resonance line broadening in heterostructures.
J. Mag. Res
Development of the 8Li cross-relaxation technique: Applications in semiconductors and other condensed matter systems
Abstract
The so-called “cross-relaxation” method is a powerful technique that can be used to provide detailed structural and site information on impurities in condensed matter systems, including semiconductors. In this paper, we report on the progress of its development at the new 8Li β-detected nuclear magnetic resonance (β-NMR) facility located in TRIUMF in Vancouver, Canada. We present first measurements using this method on a Cu single crystal and discuss future application for studies of isolated impurities in semiconductors.
Physica B, Vol 401-402, Pages 662-665
Low-field cross spin relaxation of 8Li in superconducting NbSe2
Abstract
A low energy beam of spin polarized 8Li has been used to investigate nuclear spin relaxation in the multiband superconductor NbSe2. In low magnetic fields the 1/T1 spin relaxation rate of 8Li is dominated by low frequency fluctuations in the magnetic dipolar interaction with the host 93Nb nuclear spins. We show that 1/T1 is a sensitive monitor of the static local magnetic field B just below the surface. This is used to measure the absolute value of the magnetic penetration depth λab and its temperature dependence in the Meissner state. The temperature dependence in 1/T1 and λab are consistent with a wide distribution of superconducting gaps.
Phys. Rev. B 79, 144518 (2009)
Magnetic-Field Effects of the Size of Vortices Below the Surface of NbSe2 Detected Using Low Energy β-NMR
Abstract
A low energy
radioactive beam of polarized 8Li has been used to
observe the vortex lattice below the surface of superconducting
NbSe2. The inhomogeneous magnetic field distribution
associated with the vortex lattice was measured using
depth-resolved β-detected NMR. Below Tc one observes
the characteristic lineshape from a triangular vortex lattice
which depends on the magnetic penetration depth and vortex core
radius. The size of the vortex core varies strongly with magnetic
field. In particular in a low field of 10.8 mT the core radius is
much larger than the coherence length. The possible origin of
these giant vortices is discussed.
cond-mat/0703174,
or from Phys. Rev.
Lett. 98, 167001 (2007).
Local Magnetic Properties of a Monolayer of Mn12 Single Molecule Magnets
Abstract
The magnetic
properties of a monolayer of Mn12 molecules, grafted
onto a Si substrate, have been investigated using depth-controlled
β-detected nuclear magnetic resonance. A low energy beam of spin
polarized radioactive 8Li was used to probe the local
magnetic field distribution near the Mn12 monolayer in
the Si substrate. The resonance linewidth varies strongly as a
function of implantation depth as expected from the magnetic
dipolar fields from the Mn12 electronic magnetic
moments. The temperature dependence of the linewidth indicates
that the magnetic properties of the Mn12 moments in
this low dimensional configuration differ from bulk Mn12.
Nano Lett. 7, 1551
(2007), or request preprint by email.
Hyperfine fields in an Ag/Fe multilayer film investigated with 8Li β-Detected Nuclear Magnetic Resonance
Abstract
Low energy
β-detected nuclear magnetic resonance (β-NMR) was used to
investigate the spatial dependence of the hyperfine magnetic
fields induced by Fe in the nonmagnetic Ag of an
Au(40°A)/Ag(200°A)/Fe(140°A) (001) magnetic multilayer (MML) grown
on GaAs. The resonance line-shape in the Ag layer shows dramatic
broadening compared to intrinsic Ag. This broadening is attributed
to large induced magnetic fields in this layer by the magnetic Fe
layer. We find that the induced hyperfine field in the Ag follows
a power law decay away from the Fe/Ag interface with power
−1.93(8), and a field extrapolated to 0.23(5) T at the interface.
Phys.
Rev. B 77, 144429 (2008)
β-NMR of Isolated Lithium in Nearly Ferromagnetic Palladium
Abstract
The temperature
dependence of the frequency shift and spin-lattice relaxation rate
of isolated, nonmagnetic 8Li impurities implanted in a
nearly ferromagnetic host (Pd) are measured by means of
beta-detected nuclear magnetic resonance (β-NMR). The shift is
negative, very large and increases monotonically with decreasing T
in proportion to the bulk susceptibility of Pd for T > T*~ 100
K. Below T*, an additional shift occurs which we attribute to the
response of Pd to the defect. The relaxation rate is much slower
than expected for the large shift and is linear with T below T*,
showing no sign of additional relaxation mechanisms associated
with the defect.
cond-mat/0701394,
or from Phys. Rev.
Lett. 98, 047601 (2007).
β-NMR of Isolated 8Li+ Implanted into a Thin Copper Film
Abstract
Depth-controlled
β-NMR was used to study highly spin-polarized 8Li+
in a Cu film of thickness 100 nm deposited onto a MgO substrate.
The positive Knight Shifts and spin relaxation data show that 8Li+
occupies two sites at low temperatures, assigned to be the
substitutional (S) and octahedral (O) interstitial sites. Between
50 to 100 K, there is a site change from O to S. The temperature
dependence of the Knight shifts and spin-lattice relaxation rates
at high temperatures, i.e. when all the Li are in the S site, is
consistent with the Korringa Law for a simple metal.
cond-mat/0701002,
or from Phys.
Rev.
B 75, 073405 (2007).
Near Surface Structural Phase Transition of SrTiO3 Studied with Zero Field β-Detected Nuclear Spin Relaxation and Resonance
Abstract
We demonstrate
that zero field β-detected nuclear quadrupole resonance
(β-NQR) and spin relaxation of low energy 8Li can be used as a
sensitive local probe of structural phase transitions near a
surface. We find that the transition near the surface of SrTiO3
single crystal occurs at Tc ~150 K, i.e. ~45
K higher than Tc(bulk), and that the tetragonal domains
formed below Tc are randomly oriented.
cond-mat/0511526,or
from Phys. Rev.
Lett. 96, 147601 (2006)
Nuclear Spin Relaxation of 8Li in a Thin Film of La0.67Ca0.33MnO3
Abstract
We report β-NMR measurements of the nuclear spin relaxation rate (1/T1) in a thin film of La0.67Ca0.33MnO3 (LCMO) using a low energy beam of spin polarized 8Li. In a small magnetic field of 150 G, there is broad peak in 1/T1 near the Curie temperature (Tc= 259 K) and a dramatic decrease in 1/T1 at lower temperatures. This is attributed to a critical slowing down of the spin fluctuations near Tc and freezing of the magnetic excitations at low temperatures, respectively. In addition, there is a small amplitude, slow relaxing component at high temperatures which we attribute to 8Li in the STO substrate. This is indication that the spin relaxation rate in the substrate is also peaked at Tc due to close proximity to the magnetic film. These results establish that low energy β-NMR can be used as a probe of magnetic fluctuations in magnetic thin films over a wide range of temperatures.
PDF Preprint, or
from Physica
B
374-375
(2006) 30-33.
β-NMR of Palladium Foil
Abstract
Beta-detected
NMR (β-NMR) of low energy implanted 8Li+
was studied in metallic Palladium. The resonance was found to have
a large negative shift with respect to the reference signal in the
cubic insulator MgO. This shift exhibited signi cant temperature
dependence on cooling below room temperature, approximately
proportionate to the temperature dependent spin susceptibility of
pure Pd. Thus it is tentatively attributed to a Knight shift (K)
caused by a large negative hyperfine coupling; a phenomenon common
in transition metal ions, but not in alkalis. However, the spin
lattice relaxation of 8Li is much slower than expected
from the Korringa law for such a large K. We compare results from
samples of very different thicknesses: 12.5 µm foil and a 100 nm
thin film.
PDF Preprint, or from Physica
B
374-375
(2006) 419-422.
Early 8Li+ β-NMR investigations in GaAs and Ge
Abstract
In this paper,
we describe initial studies of the structure and dynamics
associated with 8Li+ in bulk crystalline
GaAs and Ge. At low temperatures in GaAs, the amplitude of the 8Li+
resonance signal at ~3 T indicates that a large fraction (at least
70 %) of the Li end up in locations with cubic symmetry (such as
the tetrahedral interstitial and substitutional sites). The
linewidth of the β-NMR 8Li+ resonance
increases dramatically above 150 K, reaches a maximum at about 290
K, and decreases again. This suggests that the Li starts to change
its location, probably from an interstitial to a substitutional
site, at ~150 K. Experiments in Ge are also described. In this
sample, a narrow resonance is seen at low temperatures that is
likely due to Li located at an interstitial site. Near room
temperature, Li makes a transition to another site.
PDF Preprint, or from Physica B
374-375 (2006) 415-418.
β-Detected NMR of 8Li in the Normal State of 2H-NbSe2
Abstract
β-NMR of
isolated 8Li has been investigated in the normal state
of 2H-NbSe2. In a high magnetic field of 3T
a single resonance is observed with a Gaussian line
width of 3.5 kHz. The line shape varies weakly as function
of magnetic field and temperature but has a strong orientation
dependence. The nuclear electric quadrupole splitting
is unresolved implying that the electric field gradients are
10-100 times smaller than in other non-cubic crystals. The nuclear
spin relaxation rate is also anomalously small but varies linearly
with temperature as expected for Korringa relaxation in a
metal. These results suggest that Li adopts an interstitial
position between the weakly coupled NbSe2
layers and away from the conduction band.
cond-mat/0511357,
or from Physica
B
374-375
(2006) 239-242.
Beta-Detected NQR in Zero Field with a Low Energy Beam of 8Li+
Abstract
Beta-detected
nuclear quadrupole resonances (β-NQR) at zero field are observed
using a beam of low energy highly polarized radioactive 8Li+.
The resonances were detected in SrTiO3, Al2O3
and Sr2RuO4 single crystals by monitoring
the beta-decay anisotropy as a function of a small audio frequency
magnetic field. The resonances show clearly that 8Li
occupies one site with non-cubic symmetry in SrTiO3,
two in Al2O3 and three sites in Sr2RuO4.
The resonance amplitude and width are surprisingly large compared
to the values expected from transitions between the |±2> ->
|±1> spin states, indicating a significant mixing between the
|±m> quadrupolar split levels.
cond-mat/0511356,
or from Physica B 374-375 (2006) 468-471.
Abstract
A beam of low
energy 8Li has been used to probe the hyperfine
field distribution in a magnetic multilayer composed of
Au(4nm)/Ag(80nm)/Fe(2nm) grown on a GaAs substrate. The β-NMR
frequency spectrum is shown to be a strong function of the
implantation energy reflecting the depth dependence of the local
hyperfine fields. Correlating the spectra with TRIMSP implantation
profiles allows us to identify signals from the GaAs, Ag and Au
layers. The frequency spectrum in Ag is a strong function of
energy. A very narrow line, and corresponding distribution of
hyperfine fields, is observed when the beam in centered well away
from the Fe whereas a much broader distribution is observed when
the Li stops close to the Fe. These results demonstrate that low
energy β-NMR can act as a sensitive probe of the induced magnetism
in the otherwise non-magnetic Ag spacer layers.
PDF Preprint, or from Physica
B
374-375
(2006) 374-375.
Beta-Detected Nuclear Quadrupole Resonance with a Low Energy Beam of 8Li+
Abstract
A nuclear
quadrupole resonance (NQR) spectrum of 8Li has been
observed in a single crystal of SrTiO3 using a beam of
low energy highly polarized radioactive 8Li+.
The resonances were detected by monitoring the beta-decay
anisotropy as a function of a small audio frequency magnetic
field. These results demonstrate that low energy nuclear spin
polarized 8Li can be used as a sensitive probe of the
local magnetic and electronic environment in nano-structures and
ultra-thin films in zero static applied magnetic field.
PDF Preprint or from Phys. Rev. B
70, 104404 (2004)
Depth-Controlled β-NMR of 8Li in a Thin Silver Film
Abstract
We demonstrate
that β detected NMR can be used to probe the magnetic properties
of thin films and interfaces. A beam of low energy spin
polarized 8Li+ ions was implanted into a 50
nm film of Ag deposited on a SrTiO3 substrate. At
the highest fields measured (3 T), two well-resolved resonances
with different Knight shifts are observed. These lines are
attributed to Li occupying substitutional and octahedral
interstitial sites in the Ag lattice. At low magnetic fields (e.g.
0.3 T), a single narrow resonance is seen at all temperatures. The
simplicity of the spectrum suggests that a thin overlayer of Ag
can be used as a proximal magnetometer in β-NMR studies.
PDF Preprint or from Phys. Rev.
Lett 93, 157601 (2004)
The new β-NMR facility at TRIUMF and applications in semiconductors
Abstract
A new facililty
for conducting beta-detected nuclear magnetic resonance (β-NMR)
investigations of condensed matter systems has recently been
constucted at TriUniversity Meson Facility in Vancouver, Canada.
The unique features of this new facility are described, and some
preliminary results on 8Li+ in GaAs are
presented.
Physica
B
340
(2003) 1151-1154
Quadrupolar Split 8Li βNMR in SrTiO3
Abstract
We have measured the temperature dependence of the β-NMR resonances of 8Li implanted in the top few thousand Å of a crystal of SrTiO3 in a magnetic field of 3 Tesla parallel to the <100> crystal axis. A well-resolved quadrupolar splitting of the resonance is observed indicating a noncubic Li site with <100> symmetry and a quadrupolar frequency (νQ) of 153.2(4) kHz at a temperature of 211 K.The cubic-to-tetragonal crystallographic phase transition is reflected in the resonance linewidths demonstrating that β-NMR is a sensitive probe of the structure near a surface.
PDF preprint or from Physica B 326 (2003) 209-212.
8Li βNMR in Thin Metal Films
Abstract
We have measured the temperature dependence of the βNMR resonances of 8Li implanted in thin films of Au and Ag. At room temperature single narrow resonances are observed. The absence of appreciable quadrupolar splitting or broadening indicates that the Li is isolated and at a site of cubic symmetry. As the temperature is lowered, a second resonance appears which is shifted higher in frequency by ~100 ppm. We attribute the two lines to two distinct cubic sites with slightly different Knight shifts and discuss the application of this result to study fundamental phenomena exhibited by nano-confined metallic electrons.
PDF preprint or from Physica B 326 (2003) 213-216.
Range Straggling of Low Energy 8Li+ in Thin Metallic Films using βNMR
Abstract
Recently it has been demonstrated that low energy spin polarized radioactive nuclei can be used to probe the electronic and magnetic properties of ultra-thin samples using β detected NMR. However, use of the technique requires an accurate understanding of ion penetration depth and range straggling as a function of beam implantation energy and target density. Range straggling measurements of 8Li were conducted with thin films of metallic Al and Au on sapphire and SrTiO3 substrates and the results were compared to SRIM code predictions.
PDF preprint or from Physica B 326 (2003) 205-208.
Low Energy Spin Polarized Radioactive Beams as a Nano-scale Probe of Matter
Abstract
We have commissioned a polarized low energy 8Li ion beam line, which together with a high field β-NMR spectrometer, can act as sensitive new probe of thin films and interfaces. The implantation energy can be continuously adjusted from 1-90 keV and the maximum polarization achieved thus far is 80%. This instrument opens up new applications for β-NMR which parallel and complement efforts with low-energy muons. For example, it is possible to probe the magnetic field distribution near the surface of a material by stopping a polarized 8Li beam in a thin overlayer of Ag. Since the 8Li adopts a site with cubic symmetry in Ag there is no quadrupolar splitting of the resonance, and the 8Li acts as a purely magnetic sensor.
THESES:
Title:
Diffusion and surface trapping of 8Li in rutile TiO2 and the comparison on 8Li and
9Li spin relaxation using β-NMR
Author: Chatzichristos, Christos Aris
Degree Doctor of Philosophy - PhD
Program Physics
Copyright Date: 2020
Title: Beta-detected NMR
of ⁸Li⁺ in spintronic materials
Author: Song, Qun
Degree Doctor of Philosophy - PhD
Program Physics
Copyright Date: 2012
Author: Hossain, Md Masrur
Degree Doctor of Philosophy - PhD
Program Physics
Copyright Date: 2012
Title: Using low-energy ⁸Li beta-detected NMR to probe the magnetism of transition metals
Author: Parolin, Terry J.
Degree: Doctor of Philosophy - PhD
Program: Chemistry
Copyright Date: 2011
Title: Magnetic properties near the surface of cuprate superconductors studied using Beta-Detected NMR
Author: Saadaoui, Hassan
Degree: Doctor of Philosophy - PhD
Program: Physics
Copyright Date: 2009
TRIUMF Annual Report Extracts:
Some recent results may be found in the TRIUMF annual report.
For convenience, here are the βNMR contributions:
-
2006 Annual Report Contributions NbSe2(E 1095) , STO(E 1094) , Type II Superconductors(E 817) , Single Molecule Magnetic Monolayer(E 1036) , Manganites Properties(E 1040) , Finite Size Effect (E 1042) , Quantum Critical Transition(E 1041 & E 1100)
-
2005 Annual Report Contribution in PDF
-
2000 Annual Report Contribution in PDF
-
1999 Annual Report Contribution in PDF
Page last modified: 08/9/21 10:44 by Andrew MacFarlane.