Manipulation of spin Hall magnetoresistance and unidirectional spin Hall magnetoresistance in Ta/Pt/CoFeB multilayers

Abstract

The interaction between spin current and magnetic moments in heavy metal (HM)/ferromagnetic (FM) structure results in the well-known spin orbit torque and the concomitant magnetoresistance effect: spin Hall magnetoresistance (SMR) and the unidirectional SMR (USMR). In this work, we simultaneously investigated the SMR and USMR in Ta/Pt/CoFeB/MgO multilayers with different Pt thickness (tPt) by the harmonic measurements. It is observed that at tPt≈0.9nm, the SMR is close to zero and the polarity of USMR reverses, which originate from the competition of the spin current from Ta and Pt layers. Under the theoretical framework of the spin diffusion equation, we derived the theoretical expressions of SMR and USMR in the tri-layer magnetic heterostructures. We found that the tPt dependences of the SMR and USMR can be well fitted by the expressions, from which the spin transport parameters of Pt were extracted. Our work provides a fundamental insight into spin transport in the system with two heavy-metal layers, and a possible way to control SMR and USMR of HM/FM systems.