Statistical Theory of Spin Relaxation and Diffusion in Solids

A comprehensive theoretical description is given for the spin relaxation and diffusion in solids. The formulation is made in a general statistical-mechanical way. The method of the nonequilibrium statistical operator (NSO) developed by D. N. Zubarev is employed to analyze a relaxation dynamics of a spin subsystem. Perturbation of this subsystem in solids may produce a nonequilibrium state which is then relaxed to an equilibrium state due to the interaction between the particles or with a thermal bath (lattice). The generalized kinetic equations were derived previously for a system weakly coupled to a thermal bath to elucidate the nature of transport and relaxation processes. In this paper, these results are used to describe the relaxation and diffusion of nuclear spins in solids. The aim is to formulate a successive and coherent microscopic description of the nuclear magnetic relaxation and diffusion in solids. The nuclear spin-lattice relaxation is considered and the Gorter relation is derived. As an example, a theory of spin diffusion of the nuclear magnetic moment in dilute alloys (like Cu-Mn) is developed. It is shown that due to the dipolar interaction between host nuclear spins and impurity spins, a nonuniform distribution in the host nuclear spin system will occur and consequently the macroscopic relaxation time will be strongly determined by the spin diffusion. The explicit expressions for the relaxation time in certain physically relevant cases are given.Comment: 41 pages, 119 Refs. Corrected typos, added reference

Ratchet-Like Solitonic Transport in Quantum Hall Bilayers

The pseudo-spin model for double layer quantum Hall system with total landau level filling factor $\nu=1$ is discussed. Unlike the "traditional" one where interlayer voltage enters as static magnetic field along pseudo- spin hard axis, in our model we consider applied interlayer voltage as a frequency of precessing pseudo-magnetic field lying into the easy plane. It is shown that a Landau-Lifshitz equation for the considered pseudo magnetic system well describes existing experimental data. Besides that, the mentioned model predicts novel directed intra-layer transport phenomenon in the system: unidirectional intra-layer energy transport is realized due to interlayer voltage induced motion of topological kinks. This effect could be observed experimentally detecting counter-propagating intra-layer inhomogeneous charge currents which are proportional to the interlayer voltage and total topological charge of the pseudo-spin system.Comment: 4 pages, 4 figure

Two-pulse stimulated echo in magnets

The results of experimental study of two-pulse stimulated echo in ferromagnets of two types are presented. Ferromagnet Co and half-metal Co MnSi 2, in which a single-pulse echo formed by the distortion mechanism of the fronts of exciting pulse is also observed, are classified among the first type. Lithium ferrite and intermetal compound MnSb characterized by the absence of single-pulse echo in them - belong to the second type. For signals of two-pulse stimulated echo in the materials of the first type a short time and a long time of relaxations are observed. The short time is about the order of value shorter less than the spin-spin relaxation time. The long time is close to the transverse relaxation time of single-pulse echo formed by the distortion mechanism. The mechanisms that provide the possible interpretations of the peculiarities of the processes of nuclear magnetic relaxation are discussed.Comment: 10 pages, 7 figure

Theory of Sound Propagation in Superfluid Solutions Filled Porous Media

A theory of the propagation of acoustic waves in a porous medium filled with superfluid solution is developed. The elastic coefficients in the system of equations are expressed in terms of physically measurable quantities. The equations obtained describe all volume modes that can propagate in a porous medium saturated with superfluid solution. Finally, derived equations are applied to the most important particular case when the normal fluid component is locked inside a highly porous media (aerogel) by viscous forces and the velocities of two longitudinal sound modes are calculated.Comment: 13 pages, 0 figure

Ordered phase of nuclear spins in uniaxial ferromagnets at ultralow temperatures

Paper investigates the onset of nuclear magnetic ordering caused by the indirect Suhl-Nakamura interaction in ferromagnets. The necessary condition for nuclear spin ordering with definite ordering vector is obtained. Particularly, it is shown that ferromagnetically ordered phase of nuclear spins could be observed only in case of disk shaped samples. The spectrum of the nuclear spin excitations is also found