Evidence for roughness driven 90° coupling in Fe3O4/NiO/Fe3O4 trilayers

The magnetic interlayer coupling of Fe3O4 across NiO is studied using Fe3O4/NiO/Fe3O4 trilayers epitaxially grown on (001) MgO substrates. For NiO thicknesses between 0.7 and 5 nm, the magnetic moments of the two Fe3O4 layers are directed perpendicularly with respect to each other. The 90° coupling strength is determined to be 0.35±0.08mJ/m2 for a 1.4-nm-thick NiO spacer. The 90° coupling can be understood from the effect of an antiferromagnetic spacer in the presence of interface roughness.