Switching of perpendicularly polarized nanomagnets with spin orbit torque without an external magnetic field by engineering a tilted anisotropy

TLDR

Spin‑orbit torque can generate spin currents that reduce the current needed to switch nanomagnets, yet in‑plane SOT cannot deterministically switch perpendicularly polarized magnets due to symmetry, while such perpendicular magnets are preferred for high‑density storage because of their superior thermal stability. We demonstrate that a perpendicularly polarized magnet can be switched by spin‑orbit torque without an external magnetic field. By engineering a slight tilt in the magnetic easy axis of a Ta/CoFeB/MgO/Ta heterostructure, the symmetry is broken, enabling deterministic, reversible switching when the current polarity is reversed. This work introduces a new method for controlling nanomagnets with spin‑orbit torque.

Abstract

Spin orbit torque (SOT) provides an efficient way of generating spin current that promises to significantly reduce the current required for switching nanomagnets. However, an in-plane current generated SOT cannot deterministically switch a perpendicularly polarized magnet due to symmetry reasons. On the other hand, perpendicularly polarized magnets are preferred over in-plane magnets for high-density data storage applications due to their significantly larger thermal stability in ultra-scaled dimensions. Here we show that it is possible switch a perpendicularly polarized magnet by SOT without needing an external magnetic field. This is accomplished by engineering an anisotropy in the magnets such that the magnetic easy axis slightly tilts away from the film-normal. Such a tilted anisotropy breaks the symmetry of the problem and makes it possible to switch the magnet deterministically. Using a simple Ta/CoFeB/MgO/Ta heterostructure, we demonstrate reversible switching of the magnetization by reversing the polarity of the applied current. This demonstration presents a new approach for controlling nanomagnets with spin orbit torque.