STUDY OF THE NANOCRYSTALLINE FE73.5NB4.5CR5CU1B16 ALLOY BY THE RADIO-FREQUENCY-MOSSBAUER TECHNIQUE

The influence of Cr on the structural and magnetic properties of iron based amorphous and nanocrystalline alloys is studied for the Fe73.5Nb 4.5Cr5Cu1B16 alloy by ail unconventional technique which combines the Mossbauer spectroscopy with the effects induced by the radio-frequency (rf) magnetic fields (rf collapse and rf sideband effects). The nanoc rystalline bcc-Fe phase, formed by annealing the amorphous precursor f or 1 h at temperatures 490 degrees C-550 degrees C, was embedded in th e retained amorphous matrix. The conventional Mossbauer measurements a llowed the identification of three types of phases in the nanocrystall ine alloy: (i) the retained amorphous matrix, (ii) the nanocrystalline bcc-Fe phase, whose abundance increased with increasing annealing tem perature, and (iii) the interfacial phase formed at the bcc-Fe grain b oundaries. The rf collapse effect observed in the Mossbauer spectra of the samples exposed to the rf field of 60.9 MHz permits the study of the magnetic anisotropy in all phases present. The rf collapse effect occurs only in the amorphous phase, thus revealing that the magnetic a nisotropy of the amorphous matrix is significantly smaller than that e ncountered in the nanocrystalline phase. The rf-Mossbauer experiments performed as a function of the rf field intensity allowed the determin ation of the distributions of the anisotropy fields in the nanocrystal line-amorphous composite alloy. The rf sidebands effect reveals a stro ng reduction of magnetostriction related to the formation of the nanoc rystalline phase. (C) 1998 American Institute of Physics. [S0021-8979( 98)00202-3].