We discuss a joint microscopic theory for the laser-induced magnetization dynamics and spin transport in magnetic heterostructures based on the s−d interaction. Angular momentum transfer is mediated ...by scattering of itinerant s electrons with the localized (d electron) spins. We use the corresponding rate equations and focus on a ... d electron system, leading to a simplified analytical expression for the dynamics of the local magnetization that is coupled to an equation for the nonequilibrium spin accumulation of the s electrons. We show that this description converges to the microscopic three-temperature model in the limit of a strong s−d coupling. The equation for the spin accumulation is used to introduce diffusive spin transport. The presented numerical solutions show that during the laser-induced demagnetization in a ferromagnetic metal, a short-lived spin accumulation is created that counteracts the demagnetization process. Moreover, the spin accumulation leads to the generation of a spin current at the interface of a ferromagnetic and nonmagnetic metal. Depending on the specific magnetic system, both local spin dissipation and interfacial spin transport are able to enhance the demagnetization rate by providing relaxation channels for the spin accumulation that is built up during demagnetization in the ferromagnetic material. (ProQuest: ... denotes formula omitted.)
We develop a model for the magnonic contribution to the unidirectional spin Hall magnetoresistance (USMR) of heavy metal/ferromagnetic insulator bilayer films. We show that diffusive transport of ...Holstein-Primakoff magnons leads to an accumulation of spin near the bilayer interface, giving rise to a magnoresistance which is not invariant under inversion of the current direction. Unlike the electronic contribution described by Zhang and Vignale Phys. Rev. B 94, 140411 (2016), which requires an electrically conductive ferromagnet, the magnonic contribution can occur in ferromagnetic insulators such as yttrium iron garnet. We show that the magnonic USMR is, to leading order, cubic in the spin Hall angle of the heavy metal, as opposed to the linear relation found for the electronic contribution. We estimate that the maximal magnonic USMR in Pt|YIG bilayers is on the order of 10−8 but may reach values of up to 10−5 if the magnon gap is suppressed and can thus become comparable to the electronic contribution in, e.g., Pt|Co. We show that the magnonic USMR at a finite magnon gap may be enhanced by an order of magnitude if the magnon diffusion length is decreased to a specific optimal value that depends on various system parameters.
We consider the ground state of vortices in a Bose-Einstein condensate. We show that turning on a weak optical periodic potential leads to a transition from the triangular Abrikosov vortex lattice to ...phases where the vortices are pinned by the optical potential. We discuss the phase diagram of the system for a two-dimensional optical periodic potential with one vortex per optical lattice cell. We also discuss the influence of a one-dimensional optical periodic potential on the vortex ground state. The latter situation has no analog in other condensed-matter systems.
Motivated by recent experiments by Lin et al., Nature (London) 471, 83 (2011) that engineered spin-orbit coupling in ultracold mixtures of bosonic atoms, we study the dipole oscillation of trapped ...spin-orbit-coupled noncondensed Bose and Fermi gases. We find that different directions of oscillation are coupled by the spin-orbit interactions. The phase difference between oscillatory motion in orthogonal directions and the trapping frequencies of the modes are shown to be related to the anomalous Hall conductivity. Our results can be used to experimentally determine the anomalous Hall conductivity for cold-atom systems.
We consider spin-vorticity coupling-the generation of spin polarization by vorticity-in viscous two-dimensional electron systems with spin-orbit coupling. We first derive hydrodynamic equations for ...spin and momentum densities in which their mutual coupling is determined by the rotational viscosity. We then calculate the rotational viscosity microscopically in the limits of weak and strong spin-orbit coupling. We provide estimates that show that the spin-orbit coupling achieved in recent experiments is strong enough for the spin-vorticity coupling to be observed. On the one hand, this coupling provides a way to image viscous electron flows by imaging spin densities. On the other hand, we show that the spin polarization generated by spin-vorticity coupling in the hydrodynamic regime can, in principle, be much larger than that generated, e.g. by the spin Hall effect, in the diffusive regime.
Using transmission electron microscopy, we investigate the thermally activated motion of domain walls (DWs) between two positions in Permalloy (Ni80Fe20) nanowires at room temperature. We show that ...this purely thermal motion is well described by an Arrhenius law, allowing for a description of the DW as a quasiparticle in a one-dimensional potential landscape. By injecting small currents, the potential is modified, allowing for the determination of the nonadiabatic spin torque: βt=0.010±0.004 for a transverse DW and βv=0.073±0.026 for a vortex DW. The larger value is attributed to the higher magnetization gradients present.
We consider, within the framework developed by Hannay for classical integrable systems (Hannay, 1985), the geometric phases that occur in semi-classical magnetic dynamics. Such geometric phases are ...generically referred to as Hannay angles, and, in the context of magnetic dynamics, may arise as a result of both adiabatically-varying ellipticity and axis of magnetization precession. We elucidate both effects and their interplay for single-domain magnetic dynamics within a simple model with time-dependent anisotropies and external field. Subsequently, we consider spin waves and rederive, from our classical approach, some known results on what is commonly referred to as the magnon Berry phase. As an aside, these results are used to give an interpretation for geometric phases that occur in superfluids. Finally, we develop a Green’s function formalism for elliptical magnons. Within this formalism, we consider magnon transport in a mesoscopic ring and show how it is influenced by interference effects that are tuned by the Hannay angle that results from a varying ellipticity. Our results may inform the field of magnonics that seeks to utilize spin waves in applications.
PDF
