Role of structural defects on the magnetic properties of annealed Fe56Pd44 thin films upon development of the ordered L10 phase

Abstract

Fe56Pd44 thin films grown on a silicon substrate by thermal evaporation were submitted to annealing in furnace in vacuum at 550 °C for increasing time in order to transform the initial disordered fcc phase into an ordered L10 one. Starting from a detailed understanding of the time evolution of the microstructure, the complex resulting magnetic properties have been interpreted. Besides the expected increase of the coercive field due to the development of a magnetically hard phase, a non-monotonous behaviour of the remanence-to-saturation ratio has been attributed to the effects of the ordering of the developing L10 phase first, and of the progressive ordering of the alloy as a whole thereafter, once the L10 phase was already fully developed. The process of ordering of the alloy is characterised by the appearance of microstructure defects (twinned domains, twin boundaries, antiphase boundaries, polytwins), that promote a further increase of the coercive field by pinning domain walls, but also affect the remanence-to-saturation ratio and the arrangement of the magnetic domains by locally tilting and reducing the magnetic anisotropy.