(A) Study on the effect of Pt resistivity and annealing on spin-orbit torques in $Ta/Pt/Co/AlO_x$ structure

Abstract

The manipulation of the magnetization by in-plane current utilizing spin-orbit coupling has been receiving a great deal of attention due to its possible applications in non-volatile spin-orbit torque magnetic random access memory (SOT-MRAM) as well as in reprogrammable magnetic switch which can be integrated in spin logic devices. In heavy metal (HM)/ferromagnet (FM)/oxide structures, in-plane current generates spin accu-mulation at the HM/FM interfaces with spin Hall effect (SHE) and/or interfacial spin-orbit coupling (ISOC), which gives rise to a torque to the FM layer. This is known as spin-orbit torque (SOT) because the SHE and ISOC are both based on the spin-orbit coupling. There are several reports on the contribution of bulk SHE on SOTs and many researchers attempted to manipulate bulk SHE by changing thicknesses for heavy metal layer and also by changing materials for heavy metal layer since SHE is considered to be determined when the materials are chosen. However, there is little study on introducing defects or impurities into the heavy metal layer thereby changing the SHE in heavy metal layer and changing effective spin Hall angle. In this work, the defects were introduced to the Pt layer by controlling resistivity of the Pt layer through varying Pt deposition condition in an attempt to modulate the extrinsic contribution to the spin Hall effect in $Ta/Pt/Co/AlO_x$ stack. The effect of the Pt resistivity on the spin Hall effect and the SOT were studied along with the annealing effect on SOTs.