Symmetry Breaking by Materials Engineering for Spin-Orbit Torque Technology

Electric manipulation of magnetic moments is the key technology for incorporating magnetic functionalities into integrated circuits. Spin-orbit torque (SOT) arises from the spin-orbit coupling between the spin of conduction electrons and the orbital angular momentum. It is an effective tool to manipulate magnetic moments electrically. Generation of SOT requires inversion symmetry breaking which is usually achieved by spatial asymmetry. Effective application of SOT requires mirror symmetry breaking, which enables magnetization switching without an external magnetic field. In this article, we review methods of achieving these two types of symmetry breaking through material engineering. We begin by reviewing the origin of SOT and the influences of symmetry. We highlight two novel approaches to symmetry engineering. First, a bulk-like SOT is generated from a composition gradient in materials with bulk perpendicular magnetic anisotropy (PMA). Second, unconventional SOT is produced by materials with low crystal symmetry or low magnetic symmetry. We also discuss methods for conventional non-magnetic (NM)/ferromagnetic (FM) bilayers, such as tilted magnetocrystalline anisotropy and spin density gradient.

Automated summary

Electric manipulation of magnetic moments is crucial for incorporating magnetic functionalities into integrated circuits, and spin-orbit torque (SOT) provides an effective means of achieving this. The generation of SOT relies on breaking the inversion symmetry, typically achieved through spatial asymmetry. This article reviews methods for achieving symmetry breaking through material engineering, with a focus on novel approaches for generating bulk-like SOT and unconventional SOT.