Spin Seebeck Imaging of Spin-Torque Switching in Antiferromagnetic Pt/NiO Heterostructures

Isaiah Gray,Gregory D Fuchs,Katja C Nowack,Teruo Ono,Ryan Need,Brian J Kirby,Daniel C Ralph,John T Heron,Gregory M Stiehl,Darrell G Schlom,Nikhil Sivadas,Takahiro Moriyama,David H Low

doi:10.1103/physrevx.9.041016

Abstract

As electrical control of N\'eel order opens the door to reliable antiferromagnetic spintronic devices, understanding the microscopic mechanisms of antiferromagnetic switching is crucial. Spatially-resolved studies are necessary to distinguish multiple nonuniform switching mechanisms; however, progress has been hindered by the lack of tabletop techniques to image the N\'eel order. We demonstrate spin Seebeck microscopy as a sensitive, table-top method for imaging antiferromagnetic order in thin films, and apply this technique to study spin-torque switching in NiO/Pt and Pt/NiO/Pt heterostructures. We establish the interfacial antiferromagnetic spin Seebeck effect in NiO as a probe of surface N\'eel order, resolving antiferromagnetic spin domains within crystalline twin domains. By imaging before and after applying current-induced spin torque, we resolve spin domain rotation and domain wall motion, acting simultaneously. We correlate the changes in spin Seebeck images with electrical measurements of the average N\'eel orientation through the spin Hall magnetoresistance, confirming that we image antiferromagnetic order.

Highlights

Antiferromagnets (AFs), long relegated to a supporting role as the pinning layers in ferromagnetic spintronic devices [1,2], are emerging as the active element in antiferromagnetic spintronic devices [3,4,5]
We find that antiferromagnetic longitudinal spin Seebeck effect (AF LSSE) images of NiO(001) yield an order of magnitude lower voltage compared with NiO(111)
There is a potential complication interpreting the AF LSSE images in trilayers, because both Pt=NiO interfaces can contribute to the signal; we show in Supplemental Material [45] that the presence of two simultaneously contributing interfaces does not alter the interpretation of VAF LSSE as long as the AF domains are continuous in thickness, which we expect for our trilayer samples

Summary

INTRODUCTION

Antiferromagnets (AFs), long relegated to a supporting role as the pinning layers in ferromagnetic spintronic devices [1,2], are emerging as the active element in antiferromagnetic spintronic devices [3,4,5]. Recent demonstrations of the AF anomalous Nernst effect [32] and AF spin Seebeck effect [33,34] open up the possibility of using spin-thermal effects as an imaging probe, because they can be directly sensitive to Neel order [3]. We provide the first experimental demonstration of interfacial AF LSSE and use it as a direct probe of the Neel order to resolve 1–10-μm-size antiferromagnetic spin domains. By repeatedly imaging before and after spin-torque switching while varying the current density and direction in a variety of samples, we reveal effects of antidamping spin torque on the Neel order of NiO that would be difficult to establish either with device-level transport measurements or with limited beam time at an XMLD-PEEM facility. We establish the interfacial AF LSSE as the source of our signal, and we study spintorque-induced domain rotation and domain wall motion

Resolving antiferromagnetic domains in NiO

Evidence for interfacial antiferromagnetic LSSE

Findings

CONCLUSION