Non-equilibrium magnetism in dual spin valves

TL;DR

This paper demonstrates that highly non-equilibrium spin injection can alter the intrinsic magnetism of ferromagnetic materials, introducing a new mechanism beyond GMR and spin transfer torque that broadens spintronics applications.

Contribution

It reveals a novel non-equilibrium magnetism effect caused by spin injection, distinct from spin transfer torque, expanding the understanding of spintronic phenomena.

Findings

Non-equilibrium spin injection modifies ferromagnetic scattering asymmetry.

The phenomenon is distinct from spin transfer torque effects.

Potential for new spintronics applications beyond existing mechanisms.

Abstract

The field of spin electronics (spintronics) was initiated by the discovery of giant magnetoresistance (GMR) for which Fert[1] and Grunberg[2] were awarded the 2007 Nobel Prize for Physics. GMR arises from differential scattering of the majority and minority spin electrons by a ferromagnet (FM) so that the resistance when the FM layers separated by non-magnetic (NM) spacers are aligned by an applied field is different to when they are antiparallel. In 1996 Slonczewski[3] and Berger[4] predicted that a large spin-polarised current could transfer spin-angular momentum and so exert a spin transfer torque (STT) sufficient to switch thin FM layers between stable magnetisation states[5] and, for even higher current densities, drive continuous precession which emits microwaves[6]. Thus, while GMR is a purely passive phenomenon which ultimately depends on the intrinsic band structure of the FM, STT adds an active element to spintronics by which the direction of the magnetisation may be manipulated. Here we show that highly non-equilibrium spin injection can modify the scattering asymmetry and, by extension, the intrinsic magnetism of a FM. This phenomenon is completely different to STT and provides a third ingredient which should further expand the range of opportunities for the application of spintronics.