8Li spin relaxation in liquid Li alloys with compound-forming tendency

In liquid Li-Bi, Li-Pb, Li-Sn and Li-Si alloys the spinlattice relaxation rate T ₁ ^–1 of -active⁸Li (T_1/2=0.8s) probe nuclei has been measured over wide concentration (c) and temperature (T) ranges. T ₁ ^–1 is governed by hyperfine contact interaction with the conduction electrons. Near the compositions Li₃Bi, Li₄Pb, Li₄Sn and Li₄Si both (T₁T)^–1 and d(T₁T)^–1/dT versus c show marked extrema. These data, when combined with Knightshift and/or conductivity values, inform on the prolongation of the electron residence time and the reduction of the density of states at the Fermi surface. There is progressive tendency to electron localization and compound formation in the sequence Li₄Pb, Li₄Sn, Li₃Bi with mainly ionic bonding in the case of liquid Li₃Bi.This work is sponsored by the Bundesministerium für Forschung und Technologie.     

Nuclear spin relaxation rates in two-Leg spin ladders

Using the transfer-matrix density-matrix renormalization group method, we study the nuclear spin relaxation rate 1/T(1) in the two-leg s = 1 / 2 ladder as a function of the interchain (J( perpendicular)) and intrachain (J( parallel)) couplings. In particular, we separate the q(y) = 0 and pi contributions and show that the latter contribute significantly to the copper relaxation rate (63)(1/T(1)) in the experimentally relevant coupling and temperature range. We compare our results to both theoretical predictions and experimental measures on ladder materials.     

Nuclear relaxation rates for 3He adsorbed on zeolite

Transient nuclear magnetic resonance measurements of spin-lattice and spin-spin relaxation times have been carried out as a function of temperature and pressure on ³He adsorbed on two types of commercial zeolite. In addition, the number of atoms adsorbed on unit weights of zeolite was determined by spin counting. Mechanisms for spin-spin relaxation were provided by dipole interactions among helium spins and spin-lattice relaxation was probably due to atomic motion.     

Nuclear spin relaxation in disordered conductors

The relaxation timesT ₁ andT ₂ for nuclear spins interacting with the conduction electrons of disordered metals are calculated. An explicite expression for Warren's relaxation enhancement in terms of electron spectra is obtained, showing in particular that the proportionality ofT ₁ and the conductivity is a universal feature of high resistivity conductors. A formula for an inhomogeneous line width contribution due to disorder induced static Knight shift fluctuations is found. Two dimensional electron spin diffusion is shown to imply various logarithmic line width corrections.     

Nuclear spin relaxation in CoAl system

The temperature and magnetic field dependence of the nuclear spin relaxation rate $\text{1}\text{T}{}_1$ for ²⁷Al in CoAl has been investigated in the vicinity of exact stoichiometry. The experimental results are interpreted well in terms of the Benoit, de Gennes and Silhoutte (BGS) mechanism which involves a mutual flip of a nuclear spin and a localized electro spin on an excess Co atom via the Rudermann, Kittel, Kasuya and Yosida (RKKY) interaction, as well as the Korringa mechanism. The dynamic behavior of the localized moments thus obtained is discussed in terms of the Kondo effect.     

Nuclear spin relaxation in strongly disordered superconductors

The influence of nonmagnetic impurity and spin-orbit scattering on the nuclear spin-lattice relaxation rate in strongly disordered superconductors is presented. Using Anderson's exact-eigenstate formalism, it is shown that there exist two effects of disorder onT ₁ ^–1 . Firstly, nonmagnetic impurity and spin-orbit scattering enhances the magnitude of the relaxation rate in the same manner as in the normal dirty metal due to the diffusive nature of quasiparticle motion. Secondly, the Hebel-Slichter peak becomes suppressed due to the disorder enhancement of the quasiparticle inelastic scattering rate due to phonon, Coulomb, and/or spin-fluctuation interactions. Comparison with the available experimental data is made.     

Nuclear spin relaxation of Xe in liquid Te

By the method of time differential perturbed angular distribution following a nuclear reaction, the relaxation rateT _r ^–1 of the 8 msI =10⁺ isomer of¹³²Xe has been measured in liquid Te. Between 670 °K (supercooled liquid) and 1,000 °K the rate decreases from about 720/s by about a factor of two. From existing experimental material it is concluded thatT _r ^–1 is mainly due to quadrupolar interaction (T _r ^–1 T _Q ^–1 ). Its magnitude is discussed considering the metallic and the noble gas limit as models for the Xe-Te-interactions. The temperature dependenceT _Q(T) apparently does not correlate with the diffusion constant of Te in contrast to a simplified theoretical treatment. — The nuclearg value of the isomer has been determined to be g=(–)0.195(5) thus confirming the configuration (vh_11/2)².     

Nuclear spin relaxation of Xe in liquid Te

By the method of time differential perturbed angular distribution following a nuclear reaction, the relaxation rateT _r ^?1 of the 8 msI ^π=10⁺ isomer of¹³²Xe has been measured in liquid Te. Between 670 °K (supercooled liquid) and 1,000 °K the rate decreases from about 720/s by about a factor of two. From existing experimental material it is concluded thatT _r ^?1 is mainly due to quadrupolar interaction (T _r ^?1 ≈T _Q ^?1 ). Its magnitude is discussed considering the metallic and the noble gas limit as models for the Xe-Te-interactions. The temperature dependenceT _Q(T) apparently does not correlate with the diffusion constant of Te in contrast to a simplified theoretical treatment. — The nuclearg value of the isomer has been determined to be g=(?)0.195(5) thus confirming the configuration (vh_11/2)².     

Nuclear spin relaxation induced by a mechanical resonator

We report on measurements of the spin lifetime of nuclear spins strongly coupled to a micromechanical cantilever as used in magnetic resonance force microscopy. We find that the rotating-frame correlation time of the statistical nuclear polarization is set by the magnetomechanical noise originating from the thermal motion of the cantilever. Evidence is based on the effect of three parameters: (1) the magnetic field gradient (the coupling strength), (2) the Rabi frequency of the spins (the transition energy), and (3) the temperature of the low-frequency mechanical modes. Experimental results are compared to relaxation rates calculated from the spectral density of the magnetomechanical noise.     

Nuclear spin relaxation and molecular motions in sebacate polyesters

In this study, pulsed NMR techniques were used to probe the molecular motions occurring in poly(hexamethylenesebacate) (HMS), and its amorphous isomer poly(2-methyl-2-ethyl-1,3-propylenesebacate (MEPS), and in particular, to examine the perturbations in the molecular motions of HMS and MEPS that arise as a result of block copolymerization. The results show a low-temperature β-relaxation due to local motion of the methylenes of the chain backbone, an α-relaxation associated with the glass transition, and an α_c-relaxation due to the melting of the crystalline phase. Both α-and β-relaxations in the block copolymer are only slightly perturbed, and this suggests that the blocks are incompatible. The β-relaxation of HMS is confined to the amorphous regions of the polymer. Although sample preparation had little effect on the degree of crystallinity, large differences in the relaxation behavior were observed when the sample preparation was varied.     

Nuclear magnetic resonance and spin relaxation in biological systems

Proton nuclear spin-lattice relaxation in biological systems is generally distinguished from that in inorganic systems such as rocks by the presence of locally disordered macromolecular environments. Rapid exchange of readily observed labile small molecules among differently oriented macromolecular sites generally nearly averages the spectral anisotropies in the small molecule resonances. The biological tissue is generally distinguished from the inorganic matrix by the presence of a significant population of protons in the solid components that are well connected by dipolar spin couplings. Magnetic coupling between the solid and the liquid components generally dominates the magnetic field dependence of the spin-lattice relaxation rates observed in the small molecule components which is generally described by a power law in the Larmor frequency. Recent theory involving a modification of the spin-phonon class of relaxation mechanism provides a quantitative understanding of these data in terms of the dynamics of the chain molecules generally present in the solid spin systems, folded proteins for example.     

Nuclear spin lattice relaxation of191m Ir in Fe

Thermal cycling of the lattice temperature was used to determine the nuclear spin lattice relaxation of^191m IrFe in polarizing fields of 0.05 to 1.3 T. At low temperatures, the relaxation time is not very much shorter than the lifetime of^191m Ir. In the first part of the paper, the master equation formalism is extended to include a finite lifetime. Our result for the reduced relaxation constant, γ² C _K =(1.48±0.11)·10¹⁴ K s^?1 T^?2 (high field limit) is in serious disagreement with that of a spin echo measurement of¹⁹³IrFe, but fits much better into the general systematics. A comparison of relaxation rates for 3d-, 4d-, and 5d-impurities in Fe is given. As a by-product, a Kapitza conductivity constant ofl _K =1.5 mW cm^?2 K^?4±30% was found between Fe and dilute³He/⁴He.     

Muon spin relaxation in Li0.6TiO2 anode material

In Li_0.6TiO₂ the longitudinal muon spin relaxation function has been measured for temperatures between 10 and 600 K. The μSR spectra were analyzed with a Markov process for multiple collisions. The time scale found for the Li⁺ diffusion is of the order of the microsecond or shorter. Above T = 100 K the magnetic field distribution at the muon is decreasing with increasing temperature.