Interdiffusion induced high coercivity of rare-earth free Alnico/Pt thin films

Abstract Rare-earth free Alnico permanent magnet is composed of spinodally decomposed ferromagnetic L10 Fe–Co rich (α1 phase) embedded in paramagnetic or weak ferromagnetic L12 Al–Ni rich (α2 phase) matrix. We deposited α1 phase alloy (Fe52Co35.8Al5.6Ni5.3Ti0.9Cu0.4) on (111) oriented Pt (100 nm)/TiO2/SiO2/Si substrate to investigate coercivity enhancement induced by the α1 and also substrate interdiffusion through annealing. It is demonstrated that as-deposited α1 film is magnetically soft with a coercivity of ∼0.05 kOe, while its coercivity increased to 5.4 kOe after annealing at 800 °C. This is attributed to the interdiffusion between α1 phase and Pt. Therefore, a large magnetocrystalline anisotropy occurs in the tetragonal L10 (Co, Fe, Ni)Pt film.