Recent experiments have shown an indication of a hydrodynamic magnon behavior in ultrapure ferromagnetic insulators; however, its direct observation is still lacking. Here, we derive a set of coupled ...hydrodynamic equations and study the thermal and spin conductivities for such a magnon fluid. We reveal the drastic breakdown of the magnonic Wiedemann-Franz law as a hallmark of the hydrodynamics regime, which will become key evidence for the experimental realization of an emergent hydrodynamic magnon behavior. Therefore, our results pave the way toward the direct observation of magnon fluids.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UL, UM
This Letter demonstrates spin wave resonance (SWR) owing to the gyromagnetic effect by propagating a Rayleigh-type surface acoustic wave (R-SAW) through ferromagnetic thin films. The SWR amplitude in ...a NiFe film shows a higher-order frequency variation than in a magnetoelastic Ni film. This frequency dependence is well understood in terms of the presence of a gyromagnetic field attributable to the local lattice rotation in the R-SAW. From the frequency dependence of the SWR amplitude, the gyromagnetic SWR could be separated from another SWR caused by a magnetoelastic effect of the ferromagnet.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UM
We derive relativistic hydrodynamic equations with a dynamical spin degree of freedom on the basis of an entropy-current analysis. The first and second laws of local thermodynamics constrain possible ...structures of the constitutive relations including a spin current and the antisymmetric part of the (canonical) energy-momentum tensor. Solving the obtained hydrodynamic equations within the linear-mode analysis, we find spin-diffusion modes, indicating that spin density is damped out after a characteristic time scale controlled by transport coefficients introduced in the antisymmetric part of the energy-momentum tensor in the entropy-current analysis. This is a consequence of mutual convertibility between spin and orbital angular momentum.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We propose and analyze surface-plasmon-driven electron spin currents in a thin metallic film. The electron gas in the metal follows the transversely rotating electric fields of the surface plasmons ...(SPs), which leads to a static magnetization gradient. We consider herein SPs in a thin-film insulator-metal-insulator structure and solve the spin diffusion equation in the presence of a magnetization gradient. The results reveal that the SPs at the metal interfaces generate spin currents in the metallic film. For thinner film, the SPs become strongly hybridized, which increases the magnetization gradient and enhances the spin current. We also discuss how the spin current depends on SP wavelength and the spin-diffusion length of the metal. The polarization of the spin current can be controlled by tuning the wavelength of the SPs and/or the spin diffusion length.
We experimentally demonstrate the nonreciprocal generation of spin current (J_{s}) in a surface-oxidized copper film. The efficiency of conversion is at least 320 times larger than the inverse ...conversion. This nonreciprocity is due to a novel type of J_{s} generation, which relies on the transfer of angular momentum from the velocity field of free electrons. A gradient in the electrical mobility in the film produces vorticity in the in-plane drift velocity of the free electrons. The inverse process can hardly occur when J_{s} is collinear with the gradient in the electrical mobility.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UL, UM
Spin-rotation coupling, which is responsible for angular momentum conversion between the electron spin and rotational deformations of elastic media, is exploited for generating spin current. This ...method requires neither magnetic moments nor spin-orbit interaction. The spin current generated in nonmagnets is calculated in the presence of surface acoustic waves. We solve the spin diffusion equation, extended to include spin-rotation coupling, and find that larger spin currents can be obtained in materials with longer spin lifetimes. Spin accumulation induced on the surface is predicted to be detectable by time-resolved Kerr spectroscopy.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UM
General relations for nonequilibrium spin transport at a magnetic junction between a normal metal and a ferromagnetic insulator are derived from the quantum fluctuation theorem. They include the ...extended Onsager relations between the spin conductance and the spin-current noise that hold for nonequilibrium states driven by an external current. These relations are valid for a general setup of spin Hall magnetoresistance (SMR) when the main contribution is due to the interfacial spin conductance. Unidirectional spin Hall magnetoresistance (UMR) in insulating ferromagnetic junctions can be understood in a similar way. Therefore, our work can provide a comprehensive viewpoint for understanding of SMR and UMR in insulating ferromagnetic junctions. Our result also predicts relations for higher-order coefficients with respect to the external current in terms of higher-order cumulants in a unified framework.
•General relations were derived from the fluctuation theorem for nonequilibrium spin transport at a normal-metal/ferromagnetic-insulator interface.•The obtained formulas include the extended Onsager relation that holds between the spin conductance and the spin-current noise.•Our results will attribute to comprehension of the unidirectional spin Hall magnetoresistance in insulating ferromagnetic junctions.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We study the Pauli-Schrödinger equation in a uniformly rotating frame of reference to describe a coupling of spins and mechanical rotations. The explicit form of the spin-orbit interaction (SOI) with ...the inertial effects due to the mechanical rotation is presented. We derive equations of motion for a wave packet of electrons in two-dimensional planes subject to the SOI. The solution is a superposition of two cyclotron motions with different frequencies and a circular spin current is created by the mechanical rotation. The magnitude of the spin current is linearly proportional to the lower cyclotron frequency.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UM
Motivated by the recent experiment done by Yu et al. X. Z. Yu, et. al. , Sci. Adv., 6, 25, eaaz9744 (2020) on magnetic skyrmion creation and annihilation by electric currents in FeGe devices with a ...notch structure, we examine the interaction between the electric current vorticity near the notch and localized spins, and obtain three effects of the current vorticity on the localized spins. The first one is an effective Zeeman field induced by the current vorticity. This effective Zeeman field is responsible for skyrmion creation. The second effect is a vorticity-induced Dzyaloshinskii-Moriya (DM) interaction with the direction of the DM vector being parallel to the vorticity direction and is different from the vector of the intrinsic DM interaction. This vorticity-induced DM interaction makes the skyrmions distorted. The third effect is a spin current due to the gradient of the vorticity and the spin current drives the magnetic skyrmions far from the notch. Our theory opens a new path to design the magnetic textures by using structural settings.
PDF
