Effect of Bi addition on the magnetic and structural properties of chemically synthesized Fe-Pt-Ni alloy*

L1₀ FePt has been chosen as the ideal candidate for heat assisted magnetic recording media due to its high magnetocrystalline anisotropy of ~70 Merg/cc, and thermal stability down to 3 nm [1]. Producing L1₀ alloys with high thermal stability, while reducing the Curie temperature is critical for the development of heat assisted magnetic recording media, and has led to the exploration of third element doping into the L1₀ FePt [2]. In this work, we studied the effect of bismuth addition on chemically synthesized FePt_1-xNi_x alloys, with x=0.2 – 0.4. The as-made particles showed an fcc structure, but after annealing at 700^oC for 30 minutes a transformation to the L1₀ phase occurred. The addition of Bi appears to enhance the ordering of the L1₀ alloy relative to the ternary Fe-Pt-Ni but leads to the formation of a secondary phase. Thermomagnetic measurements show a reduction in Curie temperature compared to the Fe-Pt-Ni ternary alloy in the x=0.3 case, which suggests that Bi enters the structure of the L1₀ alloy. Current efforts are focused on varying the Bi content to optimize the magnetic and structural properties of Fe-Pt-Ni.

1. D. Weller and A. Moser, IEEE Trans. Magn. 36, 10 (1999).
2. Weller et. al. J. Vac Sci. Technol. B 34 (6) (2016).