Efficient Magnetization Switching via Orbital-to-Spin Conversion in Cr/W-Based Heterostructures

Abstract

A highly efficient spin–orbit torque (SOT) switching mechanism is crucial for the realization of practical SOT magnetic random-access memory (MRAM). This study proposes a Cr/W-based spin current source (SCS) that harvests the sizable orbital current from resistive Cr and results in an additional SOT through the orbital-to-spin conversion via the adjacent thin W layer. The optimal damping-like SOT efficiency can be up to −0.30 for the Cr/W heterostructure and −0.32 for the Cr/W multilayer, both of which outperform the traditional resistive W with a baseline SOT efficiency of −0.23. Additionally, the resistivity dependence of the apparent spin–orbital Hall conductivity reveals that using highly resistive Cr (>400 μΩ·cm) is the key to generating efficient orbital currents. In the cases of Cr/W heterostructure and Cr/W multilayer structures, the largely improved efficiencies also contribute to an ultralow current magnetization switching with zero-thermal current density of 1.88 and 1.54 MA/cm², expanding the utility of W-based SOT devices in high-efficiency and low-power memory applications.