Development of coercivity in Fe(Pt0.7Ni0.3)/C multilayers

The substitution of Ni for Pt in sputtered FePt/C multilayers with the aim to lower transformation temperature without much reduction in the saturation magnetization was studied. Samples were annealed at 500, 600 and 700°C. Coercivity values were observed to decrease consistently with decreasing annealing temperature. Transmission electron microscopy shows that there are well separated particles in the carbon matrix before annealing and that long time annealing leads to particle growth. Carbon serves to isolate existing particles once the particles no longer are in proximity to material available for growth. As the particle sizes are not drastically different, it is reasonable to say that chemical ordering plays a more significant role in the determination of coercivity of the FePtNi ternary system.