Ejection of boron from L10 phase for sputtered FePt-BN granular films by post-annealing

Abstract

In this study, post-annealing under NH3 gas atmosphere was conducted in order to promote the two-phase separation of FePt-BN granular films. Magnetic properties and structural analysis for the Fe50Pt50–30 vol% BN granular films revealed that (1) saturation magnetization (M s) of the granular film increased from 500 to 650 emu cm−3 with increasing post-annealing time from 0 to 10 min, (2) the orientation of FePt grains changes from (002) to (111) and fully ordered with increasing post-annealing time up to 30 min, (3) the unit cell volume of FePt grains in the granular film decreased from 55.91 to 55.55 Å3 with increasing post-annealing time from 0 to 10 min, which suggests dissolve and eject of solid solution element. From the above, M s reduction for the FePt-BN granular films is considered to be caused by the solid solution of B in the FePt grains.