Spin currents and torques via magnons, electrons, and Cooper pairs

Abstract

Spin-based electronics—spintronics—is a candidate technology for complementing or replacing traditional semiconductor electronics at the end of Moore's law. We consider different spin carriers—electrons, magnons, and Cooper pairs—and their potential for providing energy-efficient spin currents and spin torques.

In two papers we consider spin–orbit torques in synthetic antiferromagnets and van der Waals magnets. Using a collective coordinate model, we are able to explain a switching anomaly in synthetic antiferromagnets which may mitigate the dependence on an in-plane field to switch reliably using spin-Hall torques. We also find that spin–orbit torques in van der Waals magnets with trigonal prismatic symmetry may provide an accessible platform for studying the Berezinskiĭ–Kosterlitz–Thouless transition.

Joule heating is inherent to all resistive spin currents, but can be circumvented using magnons. In two further papers we consider magnonic spin-transfer in ferromagnets and multiferroics. By deriving collective coordinate equations, we clear up some of the confusion over the frequency-dependence of the domain wall velocity. In a multiferroic, we show that the domain wall velocity can be controlled using an applied electric field.

Joule heating can also be avoided by spin polarizing a supercurrent. In the two final papers we consider a superconducting spin Hall effect: the “superspin Hall effect.” We demonstrate and explain the occurrence of a transverse spin current in a ferromagnetic Josephson junction with Rashba interlayers, and consider experimental signatures of the effect. We find that the inverse superspin Hall effect can give rise to an anomalous Josephson current, and suggest that the resulting φ₀ junction can be used to directly detect the spin-polarization of a supercurrent.