Magnetic properties and microstructure of exchange coupled FePt–FeB films

Multilayers [(FexB1 − x)/FePt)]10 were deposited on a glass substrate and formed the exchange-coupled (Fe–Pt)90(FeB)10 graded film after rapid thermal annealing at 800 °C for 3 min. Out-of-plane coercivity was decreased and remanent magnetization increased when the FeB was co-doped in FePt films. When Fe content was below 40% in B, the exchange-coupled FePt–FeB films showed perpendicular magnetization with the single switching field. For higher Fe concentration (x = 0.5, 0.7, 1), easy magnetization of (001) textured FePt–FeB film was changed from perpendicular to mix-magnetization and finally to in-plane magnetization. Based on the microstructure, the FePtB film exhibits a granular structure, the FePt grains were isolated by nanocrystalline B or FeB cluster at the grain boundaries. The granular film was changed to interaction grain structure in the (FePt)90(Fe0.4B0.6)10 film. The hard-soft magnetic FePt–FeB grains formed the aggregated grains.