Dependence of magnetic properties on capping layer in magnetic multilayer structures

Abstract

Spin-orbit coupling is a recently discovered phenomenon, which explain that spin current can be ap-plied in the vertical direction of current. Many research were progressed to use it in the implementation of SOT-MRAM, a next-generation memory device. SOT-MRAM has a structure of heavy metal (HM) / magnetic layer (FM) / oxide structure and operates by the principle of controlling magnetization by using spin Hall effect. Here, torque acting on the magnetic layer is called spin-orbit torque. In order to realize the SOT-MRAM, researches have been concentrated to increase the spin-orbit torque generation efficien-cy to enable magnetization reversal at low current. Most of the experiments have been conducted mainly on the change of the thickness and material type of the heavy metal layer because the generation efficien-cy of the spin-orbital torque is determined by the spin Hall effect of the heavy metal and the Rashba effect of the heavy metal / magnetic layer interface. On the contrary, there have been few experiments to change the conditions of the magnetic layer / oxide film interface and the capping layer existing above the mag-netic layer. In 2017, the results of the DMI measurement by changing the capping layer material this June were announced. As the work function increases, DMI has increased. We expect that this would affect the magnetization reversal characteristics of the magnetic layer. The magnetic properties of the four kinds of capping layers were measured using magnetic anisotropy, spin-orbital torque, magnetization reversal, and spin Hall magnetoresistance.