# Coherent ac spin current transmission across an antiferromagnetic CoO insulator

## TL;DR

This study demonstrates that a coherent GHz ac spin current can transmit through an antiferromagnetic CoO insulator, driven by thermal magnons, enabling coherent spin precession in an adjacent ferromagnetic layer.

## Contribution

It provides experimental evidence that coherent GHz ac spin currents can pass through an AFM insulator via thermal magnons, resolving a key question in spintronics.

## Key findings

- Coherent GHz ac spin current transmits across CoO insulator.
- Thermal magnons, not evanescent spin waves, mediate the transmission.
- Coherent spin precession is driven in the ferromagnetic layer after transmission.

## Abstract

The recent discovery of spin-current transmission through antiferromagnetic (AFM) insulating materials opens up unprecedented opportunities for fundamental physics and spintronics applications. The great mystery currently surrounding this topic is: how could THz AFM magnons mediate a GHz spin current? This mis-match 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 AFM insulator and so drive the spin precession of another FM layer coherently? Utilizing element- and time-resolved x-ray pump-probe measurements on Py/Ag/CoO/Ag/Fe75Co25/MgO(001) heterostructures, we demonstrate that a coherent GHz ac spin current pumped by the permalloy (Py) ferromagnetic resonance (FMR) can transmit coherently across an antiferromagnetic CoO insulating layer to drive a coherent spin precession of the FM Fe75Co25 layer. Further measurement results favor thermal magnons rather than evanescent spin waves as the mediator of the coherent ac spin current in CoO.

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Source: https://tomesphere.com/paper/1906.00155