Field cooling-induced magnetic anisotropy in exchange biased CoO/Fe bilayer studied by ferromagneticresonance

Exchange-biased CoO/Fe bilayer grown on MgO (0 0 1) substrate by sputtering, studied by variable angle and temperature ferromagnetic resonance. Room temperature in-plane measurements reveal that the Fe layer was epitaxially grown on MgO substrate with a fourfold cubic symmetry. The data also show that the easy axis of magnetization is in the film plane and makes an angle of 45° with the [1 0 0] crystallographic direction of MgO substrate. The low temperature data exhibit a sudden onset of a field cooling-induced and shifted cubic anisotropy below the Néel temperature of CoO. This results in a twofold uniaxial or fourfold cubic symmetry for in-plane magnetic anisotropy depending on a field cooling direction. Low temperature measurements also present a reduction in the resonance fields due to the antiferromagnetic/ferromagnetic coupling. The developed theoretical model perfectly simulates the experimental data of coupled CoO/Fe bilayer.

Research highlights
► Room temperature in-plane measurements reveal that the Fe layer was epitaxially grown on MgO substrate with a fourfold cubic symmetry.
► Upon cooling the sample down to 4.2 K the CoO layer becomes antiferromagnetically ordered with the spin axes almost parallel to the Fe magnetization.
► Depending on the field cooling direction in-plane FMR data present uniaxial twofold or fourfold cubic symmetry.
► The developed theoretical model nicely fits the temperature-dependent FMR measurements of exchange-biased antiferromagnetic/ferromagnetic system.