Preferential selection of variants in ferromagnetic Fe-Pd alloys under magnetic field

Abstract
Effect of magnetic field on microstructure formation through a disorder-order transformation has been studied in FePd alloy. Single crystal of the disordered Fe-55at%Pd is subjected to an ordering heat-treatment under a magnetic field. When the ordering heat-treatment is performed without applying a magnetic field, three lattice corresponding variants are formed equivalently. On the other hand, when the ordering heat-treatment is made under a magnetic field of 4 T and higher applied along the [001] direction of the disordered phase, a single variant with an easy axis along the field direction is obtained. A tweed microstructure has been observed at early stage of ordering with streaks in the <011> directions. High density of antiphase boundary after formation of a single variant indicates the formation of homogeneous nucleation of the ordered L1₀ phase in a disordered fcc matrix at the early stage of ordering.