Structural and magnetic study of mechanically alloyed Fe-Ni

The FexNi100-x (x = 50, 65 and 80) alloys were synthesized in a conventiona l horizontal low energy bah mill. The X-ray diffraction was used to identif y and characterise Various phases during the milling process of the Fe80Ni2 0 alloy exhibiting a bcc structure whereas for x = 65 and 50 the fee struct ures are found. The steady state grain size is about 10 nm. Magnetisation m easurements after various milling periods allow to monitor a rate at which Ni atoms dissolve in the iron lattice. The room temperature values of the e ffective magnetic moment raise with the increasing milling period. All the alloys studied exhibit the ferromagnetic ordering. The magnitude of the mag netic interactions is moderately suppressed at prolonged milling as reveale d by the Curie temperatures reduced down to 950 K. Such variations are caus ed by the deviations in the interatomic arrangements of atoms especially in the intergrain regions. The Moessbauer spectroscopy confirmed the ferromag netic ordering and was used to calculate the distribution of hyperfine magn etic fields. The mean hyperfine fields are 33.8 T for Fe80Ni20 and correspo nd to the one to two Ni atoms in nearest neighbourhood. In the remaining al loys, at most, five Ni atoms are located in a neighbourhood of the Fe atom. (C)1999 Acta Metallurgica Inc.