Mossbauer study of the magnetic properties of nanocrystalline Fe80.5Nb7B12.5 alloy

The nanocrystalline body-centered-cubic (bcc)-Fe phase was formed by contro lled 1 h annealing of the amorphous Fe80.5Nb7B12.5 alloy at temperatures ra nging from 490 to 650 degrees C. The microstructure and magnetic properties of the nanocrystalline alloy were investigated by Mossbauer spectroscopy, differential scanning calorimetry, and quasistatic hysteresis loop measurem ents. Conventional Mossbauer spectroscopy allowed identification of phases and the determination of their relative content. The specialized radio freq uency (rf)-Mossbauer technique, which employs the effects induced by the rf magnetic field (rf collapse and rf sideband effects) allowed us to disting uish the magnetically soft amorphous and nanocrystalline phase from the mag netically harder microcrystalline Fe. The rf-Mossbauer experiments performe d as a function of the rf field intensity allowed determination of the anis otropy fields in each phase of the nanocrystalline alloy (amorphous matrix, nanoscale bcc-Fe grains). The measurements of the hysteresis loops versus annealing temperature revealed minimum coercivity (0.15 Oe) at 610 degrees C. (C) 1999 American Institute of Physics. [S0021-8979(99)24408-8].