Spin pumping and spin transfer

Abstract

Spin pumping is the emission of a spin current by a magnetization dynamics while spin transfer stands for the excitation of magnetization by spin currents. Using Onsager's reciprocity relations we prove that spin pumping and spin-transfer torques are two fundamentally equivalent dynamic processes in magnetic structures with itinerant electrons. We review the theory of the coupled motion of the magnetization order parameter and electron for textured bulk ferromagnets (e.g. containing domain walls) and heterostructures (such as spin valves). We present first-principles calculations for the material-dependent damping parameters of magnetic alloys. Theoretical and experimental results agree in general well. Contents

Dirac spin-orbit torques and charge pumping at the surface of topological insulators

“…While a charge current can exert a torque on the local magnetization, a precessing magnetization can pump a charge current [65,66]. These two effects are related to each other via the Onsager reciprocity relation and can be treated on equal footing.…”

Spin superfluid Josephson quantum devices

“…The fact that the same coefficient ϑ enters both Eqs. (1) and (2) is a consequence of Onsager reciprocity 8 . In Eq.…”

“…In analogy with conventional superfluidity, coupling two such magnets gives rise to the magnetic Josephson effect involving dissipationless (superfluid) flow of spin angular momentum between the magnets 7 . Spin Hall phenomenology is often discussed in the context of a bilayer system consisting of a normal metal with strong spin-orbit coupling and an insulating ferromagnet 8 . The combination of spin-orbit coupling in the metal and exchange coupling (between the conduction electron spins and the magnetic moments in the insulator) at the metal|magnet interface allow angular momentum to be transferred from the metal's crystal lattice to the ferromagnet, thus engendering macroscopic coupling between the electrical current in the metal and the magnetic order parameter 9 .…”

Spin Hall effects in metallic antiferromagnets – perspectives for future spin-orbitronics

“…A (anti)damping-like torque arises because if a spin current is injected into a FM, it is the component of the spin that is not collinear to the magnetization that is absorbed. 12 The experiments that utilize the SHE as an agent of STT follow a useful experimental approach that was established by Liu et al, where the SHE in Pt was used to exert a STT on an adjacent permalloy (Py) layer. 4 More specifically, the experiments tend to use bilayer samples where a spin Hall metal and ferromagnetic metal are fabricated directly on top of one another.…”