Coherent ac spin current transmission across an antiferromagnetic CoO insulator

Q Li,D Hou,T Y Wang,P Shafer,E Arenholz,J Li,Z Q Qiu,C Klewe,N Gao,C Hwang,A T N’Diaye,E Saitoh,R J Hicken,M Yang

doi:10.1038/s41467-019-13280-5

Abstract

The recent discovery of spin current transmission through antiferromagnetic insulating materials opens up vast opportunities for fundamental physics and spintronics applications. The question currently surrounding this topic is: whether and how could THz antiferromagnetic magnons mediate a GHz spin current? This mismatch of frequencies becomes particularly critical for the case of coherent ac spin current, raising the fundamental question of whether a GHz ac spin current can ever keep its coherence inside an antiferromagnetic insulator and so drive the spin precession of another ferromagnet layer coherently? Utilizing element- and time-resolved x-ray pump-probe measurements on Py/Ag/CoO/Ag/Fe75Co25/MgO(001) heterostructures, here we demonstrate that a coherent GHz ac spin current pumped by the Py ferromagnetic resonance can transmit coherently across an antiferromagnetic CoO insulating layer to drive a coherent spin precession of the Fe75Co25 layer. Further measurement results favor thermal magnons rather than evanescent spin waves as the mediator of the coherent ac spin current in CoO.

Highlights

The recent discovery of spin current transmission through antiferromagnetic insulating materials opens up vast opportunities for fundamental physics and spintronics applications
It is believed that the spin current propagation in AFM insulators is governed by THz magnons[12], which poses a great challenge for coherent GHz ac spin current injection e.g., by ferromagnetic resonance (FMR)[13]
FMR damping measurements indicate the injection of a GHz coherent ac spin current into an AFM layer[4,18,19,20,21], direct pump-probe measurements reveal that magnons in AFM insulators can carry net spins only in the THz range[22]

Summary

Introduction

The recent discovery of spin current transmission through antiferromagnetic insulating materials opens up vast opportunities for fundamental physics and spintronics applications. To separate the interlayer coupling and the spin current contributions, we measured the temperature dependence of the Fe75Co25 precession amplitude normalized to the Py precession amplitude (AFeCo/APy).

Results

Conclusion