Nanosized amorphous alloy powders ofFe20Ni80,Fe40Ni60,andFe60Ni40were prepared by sonochemical decomposition of solutions of volatile organic precursors,Fe(CO)5andNi(CO)4in decalin, under an argon pressure of 100 to 150 kPa at 273 K. Magnetic susceptibility ofFe40Ni60andFe60Ni40indicates blocking temperatures of 35 K and a magnetic particle size of about 6 nm. Thermogravimetric measurements ofFe20Ni80give Curie temperatures of 322 °C for amorphous and 550 °C for crystallized forms. Differential scanning calorimetry exhibits an endothermic transition at 335 °C from a combination of the magnetic phase transition and alloy crystallization. The Mo¨ssbauer spectrum of crystallizedFe20Ni80shows a sextet pattern with a hyperfine field of 25.04 T. ©1997 American Institute of Physics.