The effect of ageing on magnetic domain configurations in an iron-48% chromium alloy

Abstract

Magnetic domain configurations have been observed in an unaged and in an aged 47.8 at.% Cr-Fe alloy using transmission electron microscopy techniques. In the unaged alloy, which is a homogeneous body-centred cubic solid solution, the magnetic domain structure is quite regular, as expected for a material possessing a positive magnetocrystalline anisotropy constant. In the aged alloy the magnetic domains become much finer and highly irregular. This behaviour is associated with the formation of an inhomogeneous configuration of coherent, non-magnetic chromium-rich precipitates in a ferromagnetic iron-rich matrix. Magnetostatic energy contributions associated with the free magnetic poles originating at the precipitate-matrix interface, and magnetoelastic effects due to stress fields generated in the matrix by the precipitates, are postulated to result in local irregular rotations of the magnetization out of its easy direction, as determined by magnetocrystalline anisotropy energy considerations alone. This in turn results in an irregular domain configuration. The extent to which these effects are felt depends on foil orientation and is discussed in some detail.