A Multi-Bit-Per-Cell Memory Device Based on the Unidirectional Spin Hall Magnetoresistance

A multilayer structure comprising FM/NM/FM layers enhances the amplitude of the unidirectional spin Hall magnetoresistance (USMR) thanks to an additional FM/NM layer interface. The USMR can be used to detect the in-plane magnetization direction of each FM layer perpendicular to the current injection. Detection relies on second harmonic resistance measurements driven by the USMR with possible contribution of Joule heating-induced magnetothermal effects (ANE and SSE). The four different magnetization states (, , , ), of the FM/NM/FM layers give rise to four unique resistance levels, which can be read out by a simple two-terminal electric measurement. As a result, this FM/NM/FM multilayer structure can be used in a lateral, two-terminal device to store multiple magnetic bits. Moreover, the magnetic states can be manipulated by spin-orbit torques, opening the possibility for all-electrical operation.