Korringa-like Relaxation Research Articles

Ionic and electronic properties of the topological insulator Bi2Te2Se investigated via β -detected nuclear magnetic relaxation and resonance of Li8

We report measurements on the high temperature ionic and low temperature electronic properties of the 3D topological insulator Bi$_2$Te$_2$Se using ion-implanted $^8$Li $\beta$-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 ~150 K, spin-lattice relaxation measurements reveal isolated $^8$Li$^{+}$ diffusion with an activation energy $E_{A} = 0.185(8)$ eV and attempt frequency $\tau_{0}^{-1} = 8(3) \times 10^{11}$ s$^{-1}$ for atomic site-to-site hopping. At lower temperature, we find a linear Korringa-like 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 freezeout 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.

Gd3+ spin–lattice relaxation via multi-band conduction electrons in Y1−xGdxIn3: an electron spin resonance study

Interest in the electronic structure of the intermetallic compound YIn3 has been renewed with the recent discovery of superconductivity at T ∼ 1 K, which may be filamentary in nature. In this work we perform electron spin resonance (ESR) experiments on Gd3+ doped YIn3 (Y1−xGdxIn3; 0.001 ⪅ x ⩽̸ 0.08), showing that the spin–lattice relaxation of the Gd3+ ions, due to the exchange interaction between the Gd3+ localized magnetic moment and the conduction electrons (ce), is processed via the presence of s-, p- and d-type ce at the YIn3 Fermi level. These findings are revealed by the Gd3+ concentration dependence of the Korringa-like relaxation rate and g-shift (Δg = g − 1.993), that display bottleneck relaxation behavior for the s-electrons and unbottleneck behavior for the p- and d-electrons. The Korringa-like relaxation rates vary from 22(2) Oe/K for x ⪅ 0.001 to 8(2) Oe/K for x = 0.08 and the g-shift values change, respectively, from a positive Δg = +0.047(10) to a negative Δg = −0.008(4). Analysis in terms of a three-band ce model allows the extraction of the corresponding exchange interaction parameters Jfs, Jfp and Jfd.

LOCAL MAGNETIC BEHAVIOR OF 54Fe in EuFe2As2 AND Eu0.5K0.5Fe2As2: MICROSCOPIC STUDY USING TIME DIFFERENTIAL PERTURBED ANGULAR DISTRIBUTION (TDPAD) SPECTROSCOPY

In this paper, we report the time differential perturbed angular distribution measurements of 54 Fe on a polycrystalline EuFe 2 As 2 and Eu 0.5 K 0.5 Fe 2 As 2. The hyperfine field and nuclear spin-relaxation rate are strongly temperature dependent in the paramagnetic state suggesting strong spin fluctuation in the parent compound. The local susceptibility show Curie–Weiss-like temperature dependence and Korringa-like relaxation in the tetragonal phase indicating the presence of local moment. In the orthorhombic phase, the hyperfine field behavior suggesting quasi two-dimensional magnetic ordering. The experimental results are in a good agreement with first-principle calculations based on density functional theory.

Electron spin resonance of the intermetallic antiferromagnet EuIn2As2

We present electron spin resonance (ESR) measurements in single-crystalline samples of EuIn${}_{2}$As${}_{2}$ grown using the In-flux method. This compound crystallizes in a hexagonal P6(3)/$mmc$ structure and presents antiferromagnetic (AFM) ordering below ${T}_{N}=16$ K. In the paramagnetic state, a single Eu${}^{2+}$ Dysonian ESR line with nearly temperature-independent $g$-factor and linewidth is observed, indicating the absence of Korringa-like relaxation of the Eu${}^{2+}$ ions. Approaching the AFM transition, we observe an anisotropic $g$-shift and a linewidth broadening which has a maximum at ${T}_{N}$, suggesting that the short-range AFM correlation dominates the spin dynamics of the Eu${}^{2+}$ spins in this temperature range. Our results are discussed based on complementary data (magnetic susceptibility, heat capacity, and electrical resistivity measurements) that provide further details about the global macroscopic physical properties of the EuIn${}_{2}$As${}_{2}$ intermetallic compound.

Nuclear spin-lattice relaxation inn-type insulating and metallic GaAs single crystals

The coupling of electron and nuclear spins in $n\text{\ensuremath{-}}\mathrm{Ga}\mathrm{As}$ changes significantly as the donor concentration $n$ increases through the insulator-metal critical concentration ${n}_{\mathrm{C}}\ensuremath{\sim}1.2\ifmmode\times\else\texttimes\fi{}{10}^{16}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$. The present measurements of the $^{71}\mathrm{Ga}$ relaxation rates $W$ made as a function of magnetic field $(1--13\phantom{\rule{0.3em}{0ex}}\mathrm{T})$ and temperature $(1.5--300\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ for semi-insulating GaAs and for three doped $n\text{\ensuremath{-}}\mathrm{Ga}\mathrm{As}$ samples with donor concentrations $n=5.9\ifmmode\times\else\texttimes\fi{}{10}^{15}$, $7\ifmmode\times\else\texttimes\fi{}{10}^{16}$, and $2\ifmmode\times\else\texttimes\fi{}{10}^{18}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$, show marked changes in the relaxation behavior with $n$. Korringa-like relaxation is found in both metallic samples for $T<30\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, while for $T>30\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ phonon-induced nuclear quadrupolar relaxation is dominant. The relaxation rate measurements permit determination of the electron probability density at $^{71}\mathrm{Ga}$ sites. A small Knight shift of $\ensuremath{-}3.3\phantom{\rule{0.3em}{0ex}}\mathrm{ppm}$ was measured on the most metallic $(2\ifmmode\times\else\texttimes\fi{}{10}^{18}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3})$ sample using magic-angle spinning at room temperature. For the $n=5.9\ifmmode\times\else\texttimes\fi{}{10}^{15}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ sample, a nuclear relaxation model involving the Fermi contact hyperfine interaction, rapid spin diffusion, and exchange coupled local moments is proposed. While the relaxation rate behavior with temperature for the weakly metallic sample, $n=7\ifmmode\times\else\texttimes\fi{}{10}^{16}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$, is similar to that found for the just-insulating sample, the magnetic field dependence is quite different. For the $5.9\ifmmode\times\else\texttimes\fi{}{10}^{15}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ sample, increasing the magnetic field leads to a decrease in the relaxation rate, while for the $7\ifmmode\times\else\texttimes\fi{}{10}^{16}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ sample this results in an increase in the relaxation rate ascribed to an increase in the density of states at the Fermi level as the Landau level degeneracy is increased.

Electronic states of novel donor/acceptor type of organic superconductor, (BETS) 2(Cl 2TCNQ)

1H and 77Se NMR measurements have been performed to clarify the electronic properties of charge transfer complexes, (BETS) 2(X 2TCNQ) (X=Cl and Br). In the Cl 2TCNQ complex, a Korringa-like relaxation behavior has been observed in the metallic state at ambient pressure. At 6.5 kbar, where a metal–insulator (M–I) transition is induced, a sign of anitiferromagnetic ordering was observed in the insulating state at 10 K. In the Br 2TCNQ complex, we have also found that 77Se-1/ T 1 forms a peak around the M–I transition temperature and that NMR line is broadened in the insulating state. The nature of the insulating states of both compounds seem to be the same.

Interacting hole-spin model for oxide superconductors: NMR relaxation rate

On the basis of the interacting hole-spin model previously proposed, the temperature dependence of the longitudinal relaxation rate R of Cu NMR is calculated for the normal state. The rate is shown to consist of two terms; R=RK+RD. The term RK represents Korringa-like relaxation with strong enhancement due to the presence of 3d localized spins, and RD comes from the spin diffusion among localized 3d system. The latter is almost temperature independent. This result is in good agreement with recent experiments.

Annealing effects on the sound velocity and internal friction in the superconducting and normal states of the Cu30Zr

By means of the vibrating-reed technique we have measured the evolution upon low-temperature annealing of the internal friction ${Q}^{\mathrm{\ensuremath{-}}1}$ and sound velocity v of the ${\mathrm{Cu}}_{30}$${\mathrm{Zr}}_{70}$ amorphous alloy between 0.1 and 10 K. With an applied magnetic field of 5.6 T we measured also the normal-state behavior of both properties. Upon annealing, the internal friction and the slope of the logarithmic temperature dependence of v in the superconducting state decrease, in agreement with the standard tunneling model. Our results indicate that with thermal treatments, the coupling constant between tunneling systems (TS's) and phonons decreases, and the density of states of the TS remains constant or decreases, at most 25%, in the fully relaxed state, which is in agreement with published specific-heat results in these materials. From our data we conclude that the coupling constant between the TS and phonons should be very sensitive to the relaxed state of the disordered structure. The sound-velocity behavior strongly indicates that relaxation processes up to 10 K involve the interaction with the TS. A well-defined change of slope in v at the superconducting critical temperature ${T}_{c}$ is observed in the as-quenched and the first relaxed state, which cannot be explained with the standard tunneling model and the Korringa-like relaxation rate between the TS and electrons. Several features observed in the superconducting and normal states lead to the conclusion that the TS-electron interaction problem remains unsolved.

Field-dependent “Korringa” relaxation of protons in ZrH 2

The proton spin-lattice relaxation rate ( T 1n −1) in the transition metal hydride ZrH 2 is determined in the temperature ( T) range 40 mK ≦ T ≦ 1 K and at magnetic fields ( H) between 1 kOe and 9.5 kOe. At fixed magnetic field the product T 1n T is found to be constant, suggesting a Korringa-like relaxation process. However, T 1n depends strongly on the magnetic-field strength. In the measured field region T 1n is approximately proportional to H 3.

Enhanced Korringa-like relaxation in strongly paramagnetic rare earth-hydrogen alloys

The proton nuclear spin lattice relaxation time in several strongly paramagnetic rare earth-hydrogen alloys are found to obey a relation of the form T 1 T ∞ ( T-Θ) 2. Such a relation is shown to be consequence of assuming a generalized Korringa relation when taking into account the temperature dependence of the Knight shift.