Field-free magnetization reversal by spin-Hall effect and exchange bias

TLDR

MRAM based on spin‑transfer torque suffers from high energy dissipation, and while spin‑orbit torques and the spin‑Hall effect offer a promising alternative, deterministic switching in perpendicular magnetic anisotropy devices requires additional symmetry breaking that current in‑plane field or anisotropy‑gradient methods cannot provide. The authors aim to achieve field‑free spin‑Hall effect driven reversal in a perpendicular magnetic anisotropy device. They interface the magnetic layer with an antiferromagnetic material, creating an in‑plane exchange bias that breaks symmetry. The exchange bias enables field‑free spin‑Hall effect driven reversal of a perpendicularly magnetized Pt/Co/IrMn stack, and the experiment also reveals details of the local spin structure at the ferromagnet/antiferromagnet interface.

Abstract

Magnetic random-access memory (MRAM) driven by spin-transfer torque (STT) is a major contender for future memory applications. The energy dissipation involved in writing remains problematic, even with the advent of more efficient perpendicular magnetic anisotropy (PMA) devices. A promising alternative switching mechanism employs spin-orbit torques and the spin-Hall effect (SHE) in particular, but additional symmetry breaking is required to achieve deterministic switching in PMA devices. Currently used methods rely on in-plane magnetic fields or anisotropy gradients, which are not suitable for practical applications. Here, we interface the magnetic layer with an anti-ferromagnetic material. An in-plane exchange bias (EB) is created, and shown to enable field-free SHE-driven magnetization reversal of a perpendicularly magnetized Pt/Co/IrMn structure. Aside from the potential technological implications, our experiment provides additional insight into the local spin structure at the ferromagnetic/anti-ferromagnetic interface.