# Freezing and unfreezing of antiferromagnetic spins in CoO(111) epitaxial films on a ferromagnetic support

## TL;DR

This paper studies how antiferromagnetic spins in CoO(111) films freeze and unfreeze when paired with a ferromagnetic layer.

## Contribution

The study reveals that the blocking temperature depends on CoO thickness and involves thermal stability beyond finite-size effects.

## Key findings

- Blocking temperature depends on the thickness of the CoO layer.
- Partial unfreezing of antiferromagnetic spins allows reorientation and refreezing in new orientations.
- Findings go beyond classical finite-size effects in explaining thermal stability.

## Abstract

Epitaxial CoO(111)/Fe(110) bilayers grown on W(110) single crystal were studied using magneto-optic Kerr effect and X-ray magnetic linear dichroism techniques. A variety of possible configurations of frozen antiferromagnetic spins and in-plane easy axis of ferromagnet in CoO(111)/Fe(110) bilayers is presented. Our study shows that the blocking temperature, which marks the onset of exchange bias effect, strongly depends on the thickness of CoO layer. We confirmed that this dependence can be explained with the thermal stability of rotatable antiferromagnetic moments, that goes beyond classical finite-size effects. Partial unfreezing of antiferromagnetic spins at the vicinity of blocking temperature can be employed to reorient rotatable antiferromagnetic spins and refreeze them in a new orientation after subsequent cooling down the system.

The online version contains supplementary material available at 10.1038/s41598-025-32592-9.