Ferromagnetic domain-wall behavior during reversal and thermally activated antiferromagnetic reversal in an exchange-biased NiO/NiFe bilayer

The magnetization reversal mechanism in an exchange-biased NiO/Ni81Fe19 bilayer has been investigated using the magneto-optic Kerr effect and magnetic force microscopy imaging. The asymmetric reversal along the unidirectional axis and the two-step reversal process along the hard axis are promoted by ferromagnetic domain-wall behavior in the decreasing and increasing field branches of the as-deposited hysteresis loop, which is strongly related to the exchange coupling at the interface and the distribution of orientation of the net magnetization at the interface carried by the antiferromagnetic domains. The temperature dependence of the exchange bias and coercivity shows the thermally activated reversal of the net antiferromagnetic magnetization, which improves the unidirectional anisotropy at the interface or induces a new unidirectional axis, depending on whether the measuring field is along the unidirectional or hard axis of the as-deposited sample