Geovani Barbosa

Magnetic thermogravimetric analysis (TGM) was used to investigate the influence of the milling time (t mill) in the Curie temperature (T C) of nanocrystalline powders and of a melt-spun amorphous ribbon with composition Fe56Co7Ni7Zr10B20. The TGM analysis was carried in a continuous flow of 99.99% pure argon from room temperature up to 1250 K. A magnetic field of 100 Oe was applied throughout the measurements. Nanopowders of Fe56Co7Ni7Zr10B20 were produced by mechanical alloying the samples in an argon atmosphere for milling times ranging from 1 to 100 h. The samples were characterized by X-ray diffraction and by scanning electron microscopy. The average particle size decreased from 45.4 nm for a powder milled for 1 h to 5 nm after being milled for 100 h. Moreover, T C (=1126.4 ± 4.4 K) was found to be nearly independent of t mill while for the melt-spun amorphous ribbon it was found to be substantially smaller (T C = 482 K). This is a clear indication that T C is quite sensitive to the degree of amorphosity present in the sample. The activation energy associated to the crystallization process was estimated from DSC data by using the Kissinger’s method to be 193 kJ/mol.