Nanoscale imaging of antiferromagnetic domains in epitaxial films of CrO scanning diamond magnetic probe microscopy.

We report direct imaging of boundary magnetization associated with antiferromagnetic domains in magnetoelectric epitaxial CrO thin films using diamond nitrogen vacancy microscopy. We found a correlation between magnetic domain size and structural grain size which we associate with the domain formation process. We performed field cooling, , cooling from above to below the Néel temperature in the presence of a magnetic field, which resulted in the selection of one of the two otherwise degenerate 180° domains. Lifting of such a degeneracy is achievable with a magnetic field alone due to the Zeeman energy of a weak parasitic magnetic moment in CrO films that originates from defects and the imbalance of the boundary magnetization of opposing interfaces. This boundary magnetization couples to the antiferromagnetic order parameter enabling selection of its orientation. Nanostructuring the CrO film with mesa structures revealed reversible edge magnetic states with the direction of magnetic field during field cooling.