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

Abstract

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