Role of the interfaces in the crystallization and hysteresis mechanisms of amorphous Fe-B thin films

Highlights: • Amorphous Fe‐B thin films deposited by pulsed laser ablation for the first time. • Highly homogeneous, weak magnetic anisotropy. • No pinning involved in the magnetization reversal mechanism. • Crystallization temperature 150–250 °C lower than other Fe‐B alloys. • Negligible coercivity increase during the early crystallization stages. -- Abstract: In this work we study the crystallization processes of two sets of amorphous Fe₈₀B₂₀ films fabricated by Pulsed Laser Ablation Deposition on substrates with different nature, Corning glass® and MgO(001). We analyze their magnetic hysteresis mechanisms by means of magneto-optic techniques and Transmission Electron Microscopy. The as-deposited amorphous films present a highly homogeneous uniaxial magnetic anisotropy with the easy axis orientation dependent on the type of substrate and much weaker than that of bulk alloys with similar composition. The onset of crystallization for the films deposited on glass and MgO appears, respectively, at temperatures 150 °C and 250 °C below that of their bulk counterparts. We study the role of the substrate in the crystallization mechanism and the resulting nanostructure of the magnetic films. While the crystallization of the MgO-deposited films proceeds in a broad front growing from the substrate to the surface, that of the glass-deposited films takes place through the nucleation and growth of isolated crystallites. We analyze the evolution of the coercivity during the crystallization of the films. It follows a similar trend for both types, remaining in values close to those of the amorphous precursors until it rises steeply at a given annealing temperature. The threshold of the steep coercivity increase of the glass-deposited films is shifted to lower temperatures with respect to the MgO ones, in spite of the higher crystallization onset temperature of the former. The coercivity mechanisms have been analyzed, correlated to the films interfacial characteristics and compared to those of bulk alloys.