Crystallization and magnetic properties of Fe40Ni38B18Mo4 amorphous alloy

The crystallization behavior of heat treated amorphous Fe40Ni38B18Mo4 alloy was studied by TEM in order to investigate the suitability of this material as a soft nanostructured magnetic alloy. Significantly, the phases observed during primary and secondary crystallization were nanosized Fe-Ni solid solution and (FeNiMo)23B6, respectively. The primary crystals had an unusual irregular morphology due to the presence of molybdenum. A twinned structure was observed by nanobeam diffraction within the Fe-Ni nanocrystals. The phase transformation mechanism was compared with that of Fe40Ni40B20 and Fe40Ni40P14B6 alloys and the differences were analyzed from a thermodynamic point of view. The magnetic properties, Ms and Hc, were studied by VSM, it was found that improved soft magnetic properties were achieved by heat treatment. A mean crystal size of 10 nm and a volume fraction of 1% was found to be the microstructure which would yield the lowest coercivity.