Strong spin orientation-dependent spin current diffusion and inverse spin Hall effect in a ferromagnetic metal

Zhaozhao Zhu,Jian Su,Ying Zhang,Gang Li,Xiaoli Zheng,Jian-Wang Cai,He Bai

doi:10.1038/s41427-019-0191-1

Abstract

Pure spin current transport has become the central point of the state-of-the-art spintronics. While most spin current phenomena have been extensively explored, aspects of the pure spin current injected into ferromagnetic metals are far from completely understood. The reports on a fundamental problem, i.e. the spin relaxation asymmetry with spin current polarization collinear or transverse to the magnetization of ferromagnetic metals, are quite controversial. By employing a Y3Fe5O12 (YIG)/Cu/Ni80Fe20 (Py)/Ir25Mn75 (IrMn) spin valve heterostructure with the thermal inverse spin Hall effect (ISHE) of a Py well separated from other thermoelectric transport and thermal Hall effects, we find that the ISHE signal amplitude in 10 nm Py increases by 80% when changing the relative orientation of the YIG and Py magnetization from orthogonal (⊥) to collinear (||). Moreover, the spin-diffusion length λsf and effective spin Hall angle theta _{{mathrm{SH}}}^{{mathrm{eff}}} of Py are also spin orientation dependent and vary from lambda _{{mathrm{sf}}}^ bot = 1.0 ± 0.1 nm to lambda _{{mathrm{sf}}}^parallel = 2.8 ± 0.5 nm with theta _{{mathrm{SH}}}^{{mathrm{eff}}}left( bot right)/theta _{{mathrm{SH}}}^{{mathrm{eff}}}left( parallel right) = 1.5, respectively. Our results demonstrate magnetization orientation-dependent spin relaxation and spin injection efficiency of a pure spin current, revealing that exchange interactions in ferromagnetic metals strongly affect the transport of the pure spin current.

Highlights

In past years, pure spin current has received considerable interest in spintronics due to its non-Joule heat properties
The ferromagnetic insulator (FMI)/nonmagnetic metal (NM) bilayer is one of the most common structures for studying pure spin current phenomena, where FMI represented by Y3Fe5O12 (YIG) can generate pure spin current through magnetization precession or a temperature gradient while heavy NMs such as Pt with strong spin−orbit coupling (SOC) can serve as spin current detectors via the inverse spin Hall effect (ISHE)[1,2,3]
The validity of the SSE has been challenged by the parasitic thermal electric effect and thermal Hall effect, such as the anomalous Nernst effect (ANE)[4,5,6], magnon Hall effect (MHE)[7,8] and anomalous Righi-Leduc effect (ARLE)[9,10], it has been verified in many

Summary

Introduction

Pure spin current has received considerable interest in spintronics due to its non-Joule heat properties. When a temperature gradient is applied perpendicular to the YIG/NM interface, a magnon spin current can be NM layer because of the magnon accumulation at the YIG/NM interface, and the injected spin current in the NM is transformed into an electric voltage. This is the so-called longitudinal spin-Seebeck effect (LSSE)[3,4]. YIG-based heterostructures that LSSE remains a reliable methodology to investigate pure spin current phenomena in the framework of spin caloritronics[5,11]. The validity of the SSE has been challenged by the parasitic thermal electric effect and thermal Hall effect, such as the anomalous Nernst effect (ANE)[4,5,6], magnon Hall effect (MHE)[7,8] and anomalous Righi-Leduc effect (ARLE)[9,10], it has been verified in many

Methods

Results

Conclusion