Anomalous Hall magnetoresistance in a ferromagnet

Yumeng Yang,Shufeng Zhang,Yanjun Xu,Run-Wei Li,Haijun Wu,Ziyan Luo,Stephen J Pennycook,Yihong Wu

doi:10.1038/s41467-018-04712-9

Abstract

The anomalous Hall effect, observed in conducting ferromagnets with broken time-reversal symmetry, offers the possibility to couple spin and orbital degrees of freedom of electrons in ferromagnets. In addition to charge, the anomalous Hall effect also leads to spin accumulation at the surfaces perpendicular to both the current and magnetization direction. Here, we experimentally demonstrate that the spin accumulation, subsequent spin backflow, and spin–charge conversion can give rise to a different type of spin current-related spin current related magnetoresistance, dubbed here as the anomalous Hall magnetoresistance, which has the same angular dependence as the recently discovered spin Hall magnetoresistance. The anomalous Hall magnetoresistance is observed in four types of samples: co-sputtered (Fe1−xMnx)0.6Pt0.4, Fe1−xMnx/Pt multilayer, Fe1−xMnx with x = 0.17–0.65 and Fe, and analyzed using the drift-diffusion model. Our results provide an alternative route to study charge–spin conversion in ferromagnets and to exploit it for potential spintronic applications.

Highlights

The anomalous Hall effect, observed in conducting ferromagnets with broken time-reversal symmetry, offers the possibility to couple spin and orbital degrees of freedom of electrons in ferromagnets
When the magnetization rotates in the yzplane, an angle-dependent MR, i.e., anomalous Hall magnetoresistance (AHMR), appears and its dependence is expected to be the same as that of spin Hall magnetoresistance (SMR)
It will be of importance to confirm if the AHMR is present in others whose magnetic properties have been thoroughly investigated and well understood

Summary

Introduction

The anomalous Hall effect, observed in conducting ferromagnets with broken time-reversal symmetry, offers the possibility to couple spin and orbital degrees of freedom of electrons in ferromagnets. In the recently observed MR effects, the positive contribution does not play a role because it is insensitive to external field, while the negative contribution is modulated through controlling the amount of spin current reflection by either an adjacent magnetization (SMR and REMR) or an external magnetic field (HMR) Despite their small magnitude, these MRs are powerful tools to extract spin transport parameters, spin–orbit torque (SOT) in FM/HM heterostructures[19,20,21,22,23,24,25,26,27], which has important applications in threeterminal[20], logic[28], and sensing[29, 30] devices. Based on the drift–diffusion formalism, we derive the analytical equations for MR in a single FM layer including AHE, and demonstrate that both the magnitude and thickness dependence of AHMR can be accounted for reasonably well using the analytical model

Methods

Results

Conclusion