Field-Free Switching in Symmetry Breaking Multilayers: The Critical Role of Interlayer Chiral Exchange

TL;DR

This study demonstrates that interlayer Dzyaloshinskii-Moriya interaction (i-DMI) is essential for achieving field-free, deterministic switching in multilayer spintronic devices with perpendicular magnetic anisotropy, advancing memory technology.

Contribution

It provides a detailed investigation of i-DMI's role in symmetry breaking and current-induced switching in multilayer systems, clarifying its origin and effects in PMA and IMA layers.

Findings

i-DMI is the primary mechanism enabling field-free switching.

The effective i-DMI field decreases with stacking number.

Other mechanisms like tilted anisotropy are excluded.

Abstract

It is crucial to realize field-free, deterministic, current-induced switching in spin-orbit torque magnetic random-access memory (SOT-MRAM) with perpendicular magnetic anisotropy (PMA). A tentative solution has emerged recently, which employs the interlayer chiral exchange coupling or the interlayer Dzyaloshinskii-Moriya interaction (i-DMI) to achieve symmetry breaking. We hereby investigate the interlayer DMI in a Pt/Co multilayer system with orthogonally magnetized layers, using repeatedly stacked [Pt/Co]n structure with PMA, and a thick Co layer with in-plane magnetic anisotropy (IMA). We clarify the origin and the direction of such symmetry breaking with relation to the i-DMI effective field, and show a decreasing trend of the said effective field magnitude to the stacking number (n). By comparing the current-induced field-free switching behavior for both PMA and IMA layers, we confirm the dominating role of i-DMI in such field-free switching, excluding other possible mechanisms such as tilted-anisotropy and unconventional spin currents that may have arisen from the symmetry breaking.