Interface morphology effect on the spin mixing conductance of Pt/Fe3O4 bilayers

Thi Kim Hang Pham,Van Quang Nguyen,Sunglae Cho,Jun Hong Park,Anny Michel,Ki Hoon Kang,Nyun Jong Lee,Tae Hee Kim,Eunsang Park,Chong Seung Yoon,Mário Ribeiro

doi:10.1038/s41598-018-31915-3

Abstract

Non-magnetic (NM) metals with strong spin-orbit coupling have been recently explored as a probe of interface magnetism on ferromagnetic insulators (FMI) by means of the spin Hall magnetoresistance (SMR) effect. In NM/FMI heterostructures, increasing the spin mixing conductance (SMC) at the interface comes as an important step towards devices with maximized SMR. Here we report on the study of SMR in Pt/Fe3O4 bilayers at cryogenic temperature, and identify a strong dependence of the determined real part of the complex SMC on the interface roughness. We tune the roughness of the Pt/Fe3O4 interface by controlling the growth conditions of the Fe3O4 films, namely by varying the thickness, growth technique, and post-annealing processes. Field-dependent and angular-dependent magnetoresistance measurements sustain the clear observation of SMR. The determined real part of the complex SMC of the Pt/Fe3O4 bilayers ranges from 4.96 × 1014 Ω−1 m−2 to 7.16 × 1014 Ω−1 m−2 and increases with the roughness of the Fe3O4 underlayer. We demonstrate experimentally that the interface morphology, acting as an effective interlayer potential, leads to an enhancement of the spin mixing conductance.

Highlights

In recent years, spin currents have been a topic of intense scientific research because of its potential application in ultra-low power information technologies[1,2,3,4,5,6]
Where θSH, NM is the spin Hall angle, λNM is the spin diffusion length, σNM is the conductivity, tNM is the thickness of the NM layer, and Gr is the real part of the interface spin mixing conductance (SMC)
We followed the work of Sagasta et al.[39] where it is established that the spin relaxation in Pt follows the Elliot-Yafet mechanism, translating into a linear dependence of the spin diffusion length on the conductivity

Summary

Introduction

Spin currents have been a topic of intense scientific research because of its potential application in ultra-low power information technologies[1,2,3,4,5,6]. The SMR effect results from the spin currents generated in the NM metal via SHE that are reflected at the NM/FMI interface and converted back to a charge current via ISHE14 This additional contribution to the charge current leads to a characteristic dependence of the resistivity on the magnetization of the FMI. Within the SMR framework, maximizing the magnetoresistance requires increasing the efficiency with which spin currents flow across the NM/FMI interface[8,9,12,15,23,24,25,26,27] In this regard, it has been reported that the SMC of an NM/FMI interface can be enhanced by increasing the magnetic density at the interface. Employing the theory of SMR in NM/FMI heterostructures, we determine the real part of the SMC at the Pt/Fe3O4 interface and demonstrate that the morphology of the Fe3O4 film plays a determinant role in its magnitude

Methods

Results

Conclusion