Microstructure and Some Magnetic Properties of Nanocrystalline Fe _73.5-xCo _xCu Nb Si B Alloys

Abstract
The microstructure and magnetic properties, i.e. the initial susceptibility, coercivity and saturation magnetic polarization of nanocrystalline Fe _73.5-xCo _xCu ₁Nb ₃Si _13.5B ₉ ( x = 0 or 7) alloys with different volume fractions of crystalline and amorphous phases, are investigated. The crystalline phase in both conventionally annealed alloys (823 K for 1 h) has DO ₃ ordered structure. However, after the accumulative annealing of the samples (823 K for 5 s and then 10 and 60 min) only short range order in the crystalline phase is observed. The replacing of 7% Fe atoms by Co atoms in the Fe _73.5Cu ₁Nb ₃Si _13.5B ₉ alloy leads to the slight enhancement of the magnetic saturation polarization for both as-quenched and nanocrystalline samples. Moreover, the initial susceptibility distinctly increases and disaccommodation as well as coercivity decrease with annealing time for both investigated alloys. This behaviour is attributed to the annealing out of free volumes in the amorphous matrix and the increase of the volume fraction of the crystalline phase. Furthermore, the results reported in this paper indicate that processes occurring in the amorphous matrix are the main source of the magnetic after-effect in these alloys.