Out-of-plane angle resolved second harmonic Hall analysis in perpendicular magnetic anisotropy systems

TL;DR

This paper introduces an out-of-plane angle resolved second harmonic Hall measurement method to analyze spin orbit torques in perpendicular magnetic anisotropy systems, revealing unique torque dependencies.

Contribution

It presents a novel experimental approach for estimating SOT efficiencies and uncovers an anomalous field-like torque in Ta/CoFeB systems.

Findings

SOT efficiencies are successfully extracted using the LLGS equation.

An anomalous field-like torque dependent on magnetization direction is observed in Ta/CoFeB.

The method complements AHE-based STFMR for SOT quantification.

Abstract

Spin orbit torques (SOT) are used to manipulate magnetization of ferromagnets in heavy metal / ferromagnetic bilayers and thus are technologically relevant from magnetization switching perspective. This necessitates development of methods which give an insight into SOT behaviour and enable SOT efficiency estimation. In this article, we demonstrate an experimental approach of out-of-plane (OOP) angle resolved Second Harmonic Hall (SHH) measurement, in Pt/Co and Ta/CoFeB perpendicular magnetic anisotropy (PMA) systems, for damping-like and field-like SOT efficiency estimation. This method reveals a unique anomalous field-like torque dependent on magnetization direction in Ta/CoFeB system. The damping-like and field-like SOT efficiencies are extracted by solving LLGS equation in the low frequency limit of magnetic susceptibility. Along with SHH measurements, we also experimentally demonstrate anomalous Hall effect (AHE) based spin-torque ferromagnetic resonance (STFMR) technique for SOT efficiency quantification in PMA systems.