Magnetic anisotropy in antiferromagnetic layers affecting exchange bias of Ni–Fe/Mn–Ir bilayers

The magnetic anisotropy of antiferromagnetic layers [formula omitted] was estimated for Ni–Fe 50 Å/Mn–Ir [formula omitted] bilayers using Mauri's method [formula omitted] where [formula omitted] is the saturation value of the unidirectional anisotropy constant [formula omitted] The critical thickness of the antiferromagnetic layers [formula omitted] at which [formula omitted] took half the value of [formula omitted] was determined from the dependence of [formula omitted] on [formula omitted] The [formula omitted] was found to be almost constant [formula omitted] independent of [formula omitted] Thus, the relation of [formula omitted] was derived, suggesting that the variation in [formula omitted] is due to a change in the value of [formula omitted] [formula omitted] however, was found to vary considerably for various Mn–Ir films possessing an almost identical Ir content, and thus probably the same value of [formula omitted] In addition, studies by x-ray diffraction, transmission electron microscopy, and electron diffraction revealed that the change in [formula omitted] was independent of the microstructure and phase of the antiferromagnetic (AF) Mn–Ir films, both of which control [formula omitted] Thus, [formula omitted] was found to be independent of [formula omitted] contradicting the relation, [formula omitted] This contradiction results from the assumption by Mauri that the coupling energy (J) is equal to [formula omitted] even in the polycrystalline exchange-coupled bilayers. A model that took account of the distribution of [formula omitted] axes of AF grains in the plane of the AF film successfully explained the behavior of [formula omitted] [formula omitted] was found to change independent of both J and [formula omitted] and furthermore, it has been shown that the dependence of [formula omitted] on the sputtering conditions for Mn–Ir films is probably due to the effective temperature of the films during deposition.