Quantitative characterization of spin-orbit torques in Pt/Co/Pt /Co/Ta/BTO heterostructure on the magnetization azimuthal angle dependence

TL;DR

This paper introduces an analytical method to study how spin-orbit torque effective fields depend on the in-plane magnetization angle in heterostructures, revealing the influence of a BTO layer on the dampinglike field due to Rashba effects.

Contribution

An analytical approach is proposed to compute in-plane magnetization angle dependence of SOT effective fields, validated with experimental data on heterostructures with and without BTO layers.

Findings

Only the dampinglike field shows in-plane angle dependence in BTO-capped samples.

BTO layer induces Rashba effect, causing angular dependence of the dampinglike field.

Reference samples without BTO show no angular dependence.

Abstract

Substantial understanding of spin-orbit interactions in heavy-metal (HM)/ferromagnet (FM) heterostructures is crucial in developing spin-orbit torque (SOT) spintronics devices utilizing spin Hall and Rashba effects. Though the study of SOT effective fields dependence on the out-of-plane magnetization angle has been relatively extensive, the understanding of in-plane magnetization angle dependence remains unknown. Here, we analytically propose a method to compute the SOT effective fields as a function of the in-plane magnetization angle using harmonic Hall technique in perpendicular magnetic anisotropy (PMA) structures. Two different samples with PMA, Pt/Co/Pt/Co/Ta/BaTiO3 (BTO) test sample and Pt/Co/Pt/Co/Ta reference sample are studied using the derived formula. Our measurements reveal that only the dampinglike field of the test sample with BTO capping layer exhibits an in-plane magnetization angle dependence while no angular dependence is found in the reference sample. The presence of the BTO layer in the test sample, which gives rise to a Rashba effect at the interface, is ascribed as the source of the angular dependence of the the dampinglike field.