Spin-lattice Relaxation Rate Measurements Research Articles

Experimental nuclear quadrupole resonance and computational study of the structurally refined topological semimetal TaSb2

The local electric field gradients and magnetic dynamics of TaSb2 have been studied using Sb121, Sb123, and Ta181 nuclear quadrupole resonance (NQR) with density functional theory (DFT) calculations using XRD-determined crystal structures. By measuring all structurally expected 13 NQR lines, the nuclear quadrupole coupling constant (νQ) and asymmetric parameter (η) for Ta, Sb(1), and Sb(2) sites were obtained. These values are all in good agreement with the presented DFT calculations. Principal axes of the electric field gradients was determined for a single-crystal sample by measuring the angular dependencies of NMR frequency under a weak magnetic field. The unusual temperature dependence of η(T) of Sb(2) hints at the suppressed thermal expansion along the a axis. Spin-lattice relaxation rate (1/T1T) measurements reveal an activated-type behavior and an upturn below 30 K. Neither the low-temperature upturn nor the high-temperature activation-type behaviors are reproduced by the calculated 1/T1T based on the calculated density of states (DOS). On the other hand, the agreement between the calculated DOS and specific heat measurements indicates that the band renormalization is small. This fact indicates that TaSb2 deviates from the simple semimetal scenario, and magnetic excitations are not captured by Fermi liquid theory. Published by the American Physical Society 2024

Calorimetric measurement of nuclear spin-lattice relaxation rate in metals

The quasiparticle density of states in correlated and quantum-critical metals directly probes the effect of electronic correlations on the Fermi surface. Measurements of the nuclear spin-lattice relaxation rate provide one such experimental probe of quasiparticle mass through the electronic density of states. By far the most common way of accessing the spin-lattice relaxation rate is via nuclear magnetic resonance and nuclear quadrupole resonance experiments, which require resonant excitation of nuclear spin transitions. Here we report non-resonant access to spin-lattice relaxation dynamics in AC-calorimetric measurements. The nuclear spin-lattice relaxation rate is inferred in our measurements from its effect on the frequency dispersion of the thermal response of the calorimeter-sample assembly. We use fast, lithographically-defined nanocalorimeters to access the nuclear spin-lattice relaxation times in metallic indium from 0.3~K to 7~K and in magnetic fields up to 35~T.

Slice & Dice: nested spin-lattice relaxation measurements.

Spin-lattice relaxation rate (R1) measurements are commonly used to characterize protein dynamics. However, the time needed to collect the data can be quite long due to long relaxation times of the low-gamma nuclei, especially in the solid state. We present a method to collect backbone heavy atom relaxation data by nesting the collection of datasets in the solid state. This method results in a factor of 2 to 2.5 times faster data acquisition for backbone R1 relaxation data for the 13C and 15N sites of proteins.

Nuclear spin-lattice relaxation studies of Cu2O

We report the $^{63}\mathrm{Cu}$ and $^{65}\mathrm{Cu}$ nuclear spin-lattice relaxation rate measurements of cuprous oxide ${\mathrm{Cu}}_{2}\mathrm{O}$ in a zero field Cu nuclear quadrupole resonance at $T=77--325\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. From the detailed isotopic measurements of the relaxation rates, we successfully estimated a finite magnetic relaxation rate $^{63}W_{M}$ and a predominant nuclear quadrupole relaxation rate $^{63}W_{Q}$. $^{63}W_{Q}$ changed as ${T}^{2.1}$, whereas $^{63}W_{M}$ changed as ${T}^{1.6}$ or ${T}^{\ensuremath{\beta}}\mathrm{exp}(\ensuremath{-}\mathrm{\ensuremath{\Delta}}/\mathit{T})$ with $\ensuremath{\beta}=0.6(3)$ and $\mathrm{\ensuremath{\Delta}}=190(62)\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. The nuclear spin scattering process due to a nondegenerate Fermi gas was discussed as a possible candidate of the magnetic relaxation.

Determination of inclusion geometry of cyclodextrin host-guest complexes: Applicability of 1D selective NMR methods

The main objective of the present study is to highlight the most favourable set of 1D selective experiments based on NMR relaxation and NOE to elucidate inclusion geometry of cyclodextrin based host-guest complexes. Prediction of the mode of insertion of a model drug diflunisal (DFL) inside β-Cyclodextrin (β-CD) and 2-hydroxylpropyl-β-Cyclodextrin (HP- β-CD) has been attempted by employing one dimensional (1D) selective NMR experiments. The respective spectral complexity observed in case of β-CD and HP-β-CD inclusion complexes dictates the choice of selective measurements. A combination of non-selective (R1ns), selective (R1se) and bi-selective (R1bs) spin-lattice relaxation rate measurements has exhibited potential in quantifying molecular rotational correlation time (τc) and prediction of mode of insertion for DFL:β-CD complex while in case of DFL:HP-β-CD complex selective ROE experiment is the valid alternative to extract the inter nuclear distance data. In both the cases the fluorinated ring of DFL remains outside the CD cavity. Further, the observation of higher shift of chemical shift positions, enhanced peak intensities, slightly shorter spin-lattice relaxation times and slower molecular motion in case of HP-β-CD complex compared to the β-CD complex clearly suggested a better encapsulation of the drug by the former. In conclusion, 1D selective ROESY will be a superior method for intermediate sized CD inclusion complexes while multi-selective relaxation experiments are apt for non-intermediate sized inclusion complexes with better peak resolution.

Quasi-two-dimensional magnetic correlations inNi2P2S6probed byP31NMR

Detailed $^{31}\mathrm{P}$ nuclear magnetic resonance (NMR) measurements are presented on well-characterized single-crystals of antiferromagnetic van der Waals ${\mathrm{Ni}}_{2}{\mathrm{P}}_{2}{\mathrm{S}}_{6}$. An anomalous breakdown is observed in the proportionality of the NMR shift $K$ with the bulk susceptibility $\ensuremath{\chi}$. This so-called $K$--$\ensuremath{\chi}$ anomaly occurs in close proximity to the broad peak in $\ensuremath{\chi}(T)$, thereby implying a connection to quasi-two-dimensional (2D) magnetic correlations known to be responsible for this maximum. Quantum chemistry calculations show that crystal field energy level depopulation effects cannot be responsible for the $K$--$\ensuremath{\chi}$ anomaly. Appreciable transferred hyperfine coupling is observed, which is consistent with the proposed Ni--S--Ni super- and Ni--S--S--Ni super-super-exchange coupling mechanisms. Magnetization and spin-lattice relaxation rate (${T}_{1}^{\ensuremath{-}1}$) measurements indicate little to no magnetic field dependence of the N\'eel temperature. Finally, ${T}_{1}^{\ensuremath{-}1}(T)$ evidences relaxation driven by three-magnon scattering in the antiferromagnetic state.

Unified phase diagram of F-doped LaFeAsO by means of NMR and NQR parameters

We present $^{75}$As Nuclear Magnetic and Quadrupole Resonance results (NMR, NQR) on a new set of LaFeAsO$_{1-x}$F$_x$ polycrystalline samples. Improved synthesis conditions led to more homogenized samples with better control of the fluorine content. The structural$\equiv$nematic, magnetic, and superconducting transition temperatures have been determined by NMR spin-lattice relaxation rate and AC susceptibility measurements. The so-determined phase diagram deviates from the published one especially for low F-doping concentrations. However, if the doping level is determined from the NQR spectra, both phase diagrams can be reconciled. The absence of bulk coexistence of magnetism and superconductivity and a nanoscale separation into low-doping-like and high-doping-like regions have been confirmed. Additional frequency dependent intensity, spin-spin, and spin-lattice relaxation rate measurements on underdoped samples at the boundary of magnetism and superconductivity indicate that orthorhombicity and magnetism originate from the low-doping-like regions, and superconductivity develops at first in the high-doping-like regions.

In vitro interaction of organophosphate metabolites with bovine serum albumin: A comparative 1H NMR, fluorescence and molecular docking analysis

Since the exposure of organophosphate pesticides are known to cause severe health consequences, it is important to understand the molecular interaction of these pesticides metabolites with vital biomolecules, especially with the proteins. Here, considering bovine serum albumin (BSA) as a model protein, we have examined its interaction with two selected organophosphate metabolites, 3,5,6-trichloro-2-pyridinol (TCPy) and paraoxon methyl (PM). TCPy and PM are resultant metabolites of two most widely used organophosphate pesticides chlorpyrifos and parathion respectively. 1H NMR line broadening, selective spin-lattice relaxation rate measurements, saturation transfer difference (STD) NMR of both TCPy and PM were carried out in the presence and absence of BSA. The obtained values of the affinity index (A), binding constants (Ka) and thermodynamic parameters indicated strong organophosphates-BSA interaction. Further, fluorescence quenching data on TCPy-BSA and PM-BSA interactions strongly supported the NMR results, besides providing the stoichiometry of these complexes. Molecular docking analysis unraveled viable, strong hydrogen bonds and electrostatic interactions in TCPy-BSA and PM-BSA complexes. This study also revealed substantial time-dependent changes in the 1H NMR intensity of PM in the presence of BSA, which suggests faster degradation of PM with increasing protein concentration during protein-metabolite interactions. The hydrolysis is attributed to the esterase-like action of BSA. The result provides key insights into the direct interaction of the organophosphate metabolites with a biologically important carrier protein, serum albumin.

Early stages of fat crystallisation evaluated by low-field NMR and small-angle X-ray scattering.

Low-field time-domain nuclear magnetic resonance (NMR; 20MHz) is commonly used in the studies of fats in the form of solid fat content (SFC) measurements. However, it has the disadvantage of low sensitivity to small amounts of crystalline material (0.5%), thus often incorrectly determining crystallisation induction times. From spin-lattice relaxation rate measurements (R1 ) during the isothermal crystallisation measurements of cocoa butter between 0.01 and 10MHz using fast field cycling NMR, we learnt previously that the most sensitive frequency region is below 1MHz. Thus, we focused on analysing our 10-kHz data in detail, by observing the time dependence of R1 and comparing it with standard SFCNMR and SFC determinations from small-angle X-ray scattering (SFCSAXS ). Although not reflecting directly the SFC, the R1 at this low frequency is very sensitive to changes in molecular aggregation and hence potentially serving as an alternative for determination of crystallisation induction times. Alongside R1 , we also show that SFCSAXS is more sensitive to early stages of crystallisation, that is, standard SFCNMR determinations become more relevant when crystal growth starts to dominate the crystallisation process but fail to pick up earlier crystallisation steps. This paper thus demonstrates the potential of studying triacylglycerols at frequencies below 1MHz for obtaining further understanding of the early crystallisation stages of fats and presents an alternative and complementary method to estimate SFC by SAXS.

Normal-state properties of the antiperovskite oxide Sr3−xSnO revealed by Sn119 -NMR

We have performed $^{119}$Sn-NMR measurements on the antiperovskite oxide superconductor Sr$_{3-x}$SnO to investigate how its normal state changes with the Sr deficiency. A two-peak structure was observed in the NMR spectra of all the measured samples. This suggests that the phase separation tends to occur between the nearly stoichiometric and heavily Sr-deficient Sr$_{3-x}$SnO phases. The measurement of the nuclear spin-lattice relaxation rate $1/T_1$ indicates that the Sr-deficient phase shows a conventional metallic behavior due to the heavy hole doping. In contrast, the nearly stoichiometric phase exhibits unusual temperature dependence of $1/T_1$, attributable to the presence of a Dirac-electron band.

Structural phase transition, antiferromagnetism and two superconducting domes in LaFeAsO1-xFx (0 < x ≤ 0.75)

We report $^{75}$As nuclear magnetic resonance (NMR) / nuclear quadrupole resonance (NQR) and transmission electron microscopy (TEM) studies on LaFeAsO$_{1-x}$F$_{x}$. There are two superconducting domes in this material. The first one appears at 0.03 $\leq$ $x$ $\leq$ 0.2 with $T_{\rm c}$$^{max}$ = 27 K, and the second one at 0.25 $\leq$ $x$ $\leq$ 0.75 with $T_{\rm c}$$^{max}$ = 30 K. By NMR and TEM, we demonstrate that a $C4$-to-$C2$ structural phase transition (SPT) takes place above both domes, with the transition temperature $T_{\rm s}$ varying strongly with $x$. In the first dome, the SPT is followed by an antiferromagnetic (AF) transition, but neither AF order nor low-energy spin fluctuations are found in the second dome. In LaFeAsO$_{0.97}$F$_{0.03}$, we find that AF order and superconductivity coexist microscopically via $^{75}$As nuclear spin-lattice relaxation rate (1/$T_1$) measurements. In the coexisting region, 1/$T_1$ decreases at $T_{\rm c}$ but becomes to be proportional to $T$ below 0.6$T_{\rm c}$, indicating gapless excitations. Therefore, in contrast to the early reports, the obtained phase diagram for $x \leq$ 0.2 is quite similar to the doped BaFe$_{2}$As$_{2}$ system. The electrical resistivity in the second dome can be fitted by $\rho = {{\rho }_{0}}+A{{T}^{n}}$ with $n$ = 1 and a maximal coefficient $A$ at around $x_{opt}$ = 0.5$\sim$0.55 where $T_{\rm s}$ extrapolates to zero and $T_{\rm c}$ is the maximal, which suggest the importance of quantum critical fluctuations associated with the SPT. We have constructed a complete phase diagram of LaFeAsO$_{1-x}$F$_{x}$, which provides insight into the relationship between SPT, antiferromagnetism and superconductivity.

Spin dynamics in the single-ion magnet [Er(W5O18)2]9−

In this work we present a detailed NMR and ${\ensuremath{\mu}}^{+}\mathrm{SR}$ investigation of the spin dynamics in the new hydrated sodium salt containing the single-ion magnet ${[\mathrm{Er}{({\mathrm{W}}_{5}{\mathrm{O}}_{18})}_{2}]}^{9\ensuremath{-}}$. The $^{1}\mathrm{H}\phantom{\rule{0.16em}{0ex}}\mathrm{NMR}$ absorption spectra at various applied magnetic fields present a line broadening on decreasing temperature which indicates a progressive spin freezing of the single-molecule magnetic moments. The onset of quasistatic local magnetic fields, due to spin freezing, is observed also in the muon relaxation curves at low temperature. Both techniques yield a local field distribution of the order of 0.1--0.2 T, which appears to be of dipolar origin. On decreasing the temperature, a gradual loss of the $^{1}\mathrm{H}\phantom{\rule{0.16em}{0ex}}\mathrm{NMR}$ signal intensity is observed, a phenomenon known as wipe-out effect. The effect is analyzed quantitatively on the basis of a simple model which relies on the enhancement of the NMR spin-spin, ${T}_{2}^{\ensuremath{-}1}$, relaxation rate due to the slowing down of the magnetic fluctuations. Measurements of spin-lattice relaxation rate ${T}_{1}^{\ensuremath{-}1}$ for $^{1}\mathrm{H}\phantom{\rule{0.16em}{0ex}}\mathrm{NMR}$ and of the muon longitudinal relaxation rate \ensuremath{\lambda} show an increase as the temperature is lowered. However, while for the NMR case the signal is lost before reaching the very slow fluctuation region, the muon spin-lattice relaxation \ensuremath{\lambda} can be followed until very low temperatures and the characteristic maximum, reached when the electronic spin fluctuation frequency becomes of the order of the muon Larmor frequency, can be observed. At high temperatures, the data can be well reproduced with a simple model based on a single correlation time $\ensuremath{\tau}={\ensuremath{\tau}}_{0}\phantom{\rule{0.16em}{0ex}}\mathrm{exp}(\mathrm{\ensuremath{\Delta}}/\mathrm{T})$ for the magnetic fluctuations. However, to fit the relaxation data for both NMR and ${\ensuremath{\mu}}^{+}\mathrm{SR}$ over the whole temperature and magnetic field range, one has to use a more detailed model that takes into account spin-phonon transitions among the $\mathrm{E}{\mathrm{r}}^{3+}$ magnetic sublevels. A good agreement for both proton NMR and ${\ensuremath{\mu}}^{+}\mathrm{SR}$ relaxation is obtained, which confirms the validity of the energy level scheme previously calculated from an effective crystal field Hamiltonian.

NMR evidence for static local nematicity and its cooperative interplay with low-energy magnetic fluctuations in FeSe under pressure

We present $^{77}$Se-NMR measurements on single-crystalline FeSe under pressures up to 2 GPa. Based on the observation of the splitting and broadening of the NMR spectrum due to structural twin domains, we discovered that static, local nematic ordering exists well above the bulk nematic ordering temperature, $T_{\rm s}$. The static, local nematic order and the low-energy stripe-type antiferromagnetic spin fluctuations, as revealed by NMR spin-lattice relaxation rate measurements, are both insensitive to pressure application. These NMR results provide clear evidence for the microscopic cooperation between magnetism and local nematicity in FeSe.

Nuclear magnetic relaxation dispersion of murine tissue for development of T1 (R1 ) dispersion contrast imaging.

This study quantified the spin-lattice relaxation rate (R1 ) dispersion of murine tissues from 0.24 mT to 3T. A combination of ex vivo and in vivo spin-lattice relaxation rate measurements were acquired for murine tissue. Selected brain, liver, kidney, muscle, and fat tissues were excised and R1 dispersion profiles were acquired from 0.24 mT to 1.0T at 37°C, using a fast field-cycling MR (FFC-MR) relaxometer. In vivo R1 dispersion profiles of mice were acquired from 1.26T to 1.74T at 37°C, using FFC-MRI on a 1.5T scanner outfitted with a field-cycling insert electromagnet to dynamically control B0 prior to imaging. Images at five field strengths (1.26, 1.39, 1.5, 1.61, 1.74T) were acquired using a field-cycling pulse sequence, where B0 was modulated for varying relaxation durations prior to imaging. R1 maps and R1 dispersion (ΔR1 /ΔB0 ) were calculated at 1.5T on a pixel-by-pixel basis. In addition, in vivo R1 maps of mice were acquired at 3T. At fields less than 1T, a large R1 magnetic field dependence was observed for tissues. ROI analysis of the tissues showed little relaxation dispersion for magnetic fields from 1.26T to 3T. Our tissue measurements show strong R1 dispersion at field strengths less than 1T and limited R1 dispersion at field strengths greater than 1T. These findings emphasize the inherent weak R1 magnetic field dependence of healthy tissues at clinical field strengths. This characteristic of tissues can be exploited by a combination of FFC-MRI and T1 contrast agents that exhibit strong relaxivity magnetic field dependences (inherent or by binding to a protein), thereby increasing the agents' specificity and sensitivity. This development can provide potential insights into protein-based biomarkers using FFC-MRI to assess early changes in tumour development, which are not easily measureable with conventional MRI.

Transient NOE enhancement in solid-state MAS NMR of mobile systems

It has been known that the heteronuclear cross-relaxation affects the dilute S spin magnetization along the longitudinal direction, causing an overshoot phenomenon for those mobile systems in spin-lattice relaxation rate measurements. Here, we analyze the Solomon equations for an I-S system and derive the transient cross relaxation effect as to when an overshoot phenomenon would take place and what the maximum enhancement could be at the time of the overshoot. In order to utilize such a transient nuclear Overhauser effect (NOE), we first time apply it to dynamic solid samples by inverting the 1H magnetization prior to the excitation of the S spin. It is found that the overshoot depends on the ratio of the I and S spin-lattice relaxation rates, i.e. RSS/RII. When RSS/RII≫1, the maximum enhancement factor for transient NOE could be larger than that obtained in steady-state NOE experiments. Furthermore, transient NOE appears to be more efficient in terms of sensitivity enhancement of dilute spins in solid-state NMR of mobile systems than the traditional cross polarization scheme whose efficiency is greatly compromised by molecular mobility. A sample of natural abundance l-isoleucine amino acid, in which the spin-lattice relaxation rates for the four methyl carbons are different, has been used to demonstrate sensitivity enhancement factors under various experimental schemes.

A model for the interpretation of nuclear magnetic resonance spin-lattice dispersion measurements on mortar, plaster paste, synthetic clay and oil-bearing shale

A model linking the molecular-scale dynamics of fluids confined to nano-pores to nuclear magnetic resonance (NMR) relaxation rates is proposed. The model is used to re-analyse fast field-cycling spin-lattice relaxation rate measurements for the separate water and oil dispersions from an oil-bearing shale [Korb et al., J. Phys. Chem. C, 118, 199 (2014)]. The model assumes that pore fluid can be characterized by three time constants: the surface and bulk diffusion correlation times and a surface desorption time constant. Results are shown to yield meaningful and consistent intra-pore dynamical time constants, insight into diffusion mechanisms and pore morphology. The shale is found to be oil-wetting and the water dispersion is found to be due to the interaction of aqueous Mn2+ ions with bulk water spins. Clay, mortar and plaster paste dispersions measurements have also been successfully re-analysed and a summary of the results is presented. The results demonstrate the wide applicability of the model which advances NMR dispersion experimentation as a powerful tool for measuring nano-porous fluid properties.

Explicit calculation of nuclear-magnetic-resonance relaxation rates in small pores to elucidate molecular-scale fluid dynamics.

Nuclear-magnetic-resonance (NMR) spin-lattice (T_{1}^{-1}) and spin-spin (T_{2}^{-1}) relaxation rate measurements can act as effective nondestructive probes of the nanoscale dynamics of ^{1}H spins in porous media. In particular, fast-field-cycling T_{1}^{-1} dispersion measurements contain information on the dynamics of diffusing spins over time scales spanning many orders of magnitude. Previously published experimental T_{1}^{-1} dispersions from a plaster paste, synthetic saponite, mortar, and oil-bearing shale are reanalyzed using a model and associated theory which describe the relaxation rate contributions due to the interaction between spin ensembles in quasi-two-dimensional pores. Application of the model yields physically meaningful diffusion correlation times for all systems. In particular, the surface diffusion correlation time and the surface desorption time take similar values for each system, suggesting that surface mobility and desorption are linked processes. The bulk fluid diffusion correlation time is found to be two to five times the value for the pure liquid at room temperature for each system. Reanalysis of the oil-bearing shale yields diffusion time constants for both the oil and water constituents. The shale is found to be oil wetting and the water T_{1}^{-1} dispersion is found to be associated with aqueous Mn^{2+} paramagnetic impurities in the bulk water. These results escalate the NMR T_{1}^{-1} dispersion measurement technique as the primary probe of molecular-scale dynamics in porous media yielding diffusion parameters and a wealth of information on pore morphology.

ChemInform Abstract: Review of NMR Studies of Nanoscale Molecular Magnets Composed of Geometrically Frustrated Antiferromagnetic Triangles

AbstractReview: 68 refs.

Diffusion-induced 7Li NMR relaxation of layer-structured tin disulphide — Li diffusion along the buried interfaces in Li0.17SnS2

7Li NMR relaxation has been used to study lithium-ion diffusion in layer-structured SnS2. Keeping the Li intercalation degree in LixSnS2 below x=0.49, the Li ions preferentially occupy sites in the van der Waals gap between the SnS2 sheets. In contrast to conventional NMR spin-lattice relaxation (SLR) rate measurements in the laboratory frame of reference, which are sensitive to rather fast Li exchange processes, with the help of spin-locking SLR NMR slower Li motions were extracted from characteristic diffusion-induced rate peaks. The latter contain information on both Li+ activation energies Ea and Li ion jump rates τ−1 characterizing the elementary steps of Li+ hopping. Our results point to two different diffusion processes (Ea(I)=0.38eV; Ea(II)=0.28eV), a slower and a faster one, observable directly after chemical Li insertion. Interestingly, the diffusion behaviour irreversibly changes when the sample has been exposed to temperatures as high as 573K. Diffusion-induced NMR rates and corresponding line shapes are discussed with respect to an inhomogenous distribution of Li ions in SnS2, which seems to be present directly after Li intercalation.

Evidence for unidimensional low-energy excitations as the origin of persistent spin dynamics in geometrically frustrated magnets

We report specific heat, magnetic, and muon spin relaxation measurements performed on a polycrystalline sample of the normal spinel CdHo2S4. The rare-earth ions sit on a lattice of corner-sharing regular tetrahedra as in pyrochlore compounds. Magnetic ordering is detected at Tc ~ 0.87 K. From spin-lattice relaxation rate measurements on both sides of Tc we uncover similar magnetic excitation modes driving the so-called persistent spin dynamics at T < Tc. Unidimensional excitations are argued to be at its origin. Often observed spin loop structures are suggested to support these excitations. The possibility of a generic mechanism for their existence is discussed.