Spin-orbit torque magnetization switching in a perpendicularly magnetized full Heusler alloy Co₂FeSi

To optimize the writing and reading performance of magnetic random-access memory (MRAM) devices, achieving current-induced spin-orbit torque (SOT) magnetization switching in perpendicularly magnetized full Heusler alloys is vitally important. For conventional SOT-metal bilayer systems, heavy metals (HMs) with a large spin Hall angle (θSH) are generally used for generating a spin current, which is injected into the adjacent ferromagnet (FM) layer and exerts a torque on the magnetization to switch it. However, the large resistivity of generally used HMs such as β-Ta and β-W can increase the Ohmic loss. In this article, we achieve full SOT switching in Heusler alloy Co2FeSi using low-resistivity Pd as a spin current generation source. The critical switching current density is found to be 3.7 × 107 A cm-2, which is in the same order of magnitude as that required for conventional HM/FM systems even though Pd has a smaller θSH than that of generally used HMs. Using harmonic Hall measurements, the damping-like and field-like effective fields per unit current density are estimated to be 56.9 (10-7 Oe A-1 cm2) and 39.8 (10-7 Oe A-1 cm2), respectively. This high efficiency can be attributed to the excellent lattice matching between Co2FeSi and Pd (only 2% mismatch), to a slight Pd diffusion, and possibly to the additional SOTs induced by the in-plane spin component generated in the Co2FeSi layer. Our finding will advance the development of SOT-MRAM devices with both better reading and writing performance.