Orbit-transfer torque driven field-free switching of perpendicular magnetization

TL;DR

This paper introduces a novel orbit-transfer torque (OTT) mechanism using orbital magnetic moments in WTe2 to achieve field-free switching of perpendicular magnetization, advancing low-power MRAM technology.

Contribution

It presents the first demonstration of current-driven, field-free perpendicular magnetization switching via OTT using orbital magnetic moments in WTe2/Fe3GeTe2 heterostructures.

Findings

OTT enables deterministic switching without external magnetic fields

Orbital magnetic moments are polarized by current in WTe2 due to Berry curvature dipole

Switching direction is controlled by current polarity

Abstract

The reversal of perpendicular magnetization (PM) by electric control is crucial for high-density integration of low-power magnetic random-access memory (MRAM). Although the spin-transfer torque (STT) and spin-orbit torque (SOT) technologies have been used to switch the magnetization of a free layer with perpendicular magnetic anisotropy, the former has limited endurance because of the high current density directly through the junction, while the latter requires an external magnetic field or unconventional configuration to break the symmetry. Here we propose and realize the orbit-transfer torque (OTT), that is, exerting torque on the magnetization using the orbital magnetic moments, and thus demonstrate a new strategy for current-driven PM reversal without external magnetic field. The perpendicular polarization of orbital magnetic moments is generated by a direct current in a few-layer WTe2 due to the existence of nonzero Berry curvature dipole, and the polarization direction can be switched by changing the current polarity. Guided by this principle, we construct the WTe2/Fe3GeTe2 heterostructures, where the OTT driven field-free deterministic switching of PM is achieved.