Structural, Microstructural and Magnetic Properties of Nanocrystalline Ni75Fe25 Compound Produced by Mechanical Alloying

The mechanical alloying process was used to prepare nanocrystalline Ni75Fe23 powders. Several milling times have been used ranging from 3 h up to 96 h. The microstructure, structure and magnetic properties were studied by scanning electron microscopy, X-ray diffraction, and hysteresis measurements. From X-ray diffraction spectra, we showed that the Ni3Fe phase starts to form after 6 h milling time and dominates after 24 h of milling. When the milling time increases, the grain size decreases to 14 nm, the mean level of microdistorsions increases to 0.67%. The SEM images taken at different milling time allowed us to follow the morphology of the materials at different stages. Elemental mapping experiments (EDX) indicate that the Fe and Ni elemental distributions are closely correlated indicating that the two elements are completely alloyed and the Ni(Fe) solid solution is formed at 24 h of milling time. From hysteresis curves, we derived the saturation magnetization, M-s, and the coercive field, H-c. It is observed that M-s monotonously increases with increasing milling time. This increase in M-s may be attributed to the completion of alloying process and also to the reduction of magnetocrystalline anisotropy due to the grain refinement. For milling times larger than 3 h, H-c sharply decreases and reaches a minimum value of 5 Oe after 96 h. The decrease of Fic is. attributed to the decrease in the grain size. We show that nanocrystalline Ni73Fe23 powder exhibits a soft magnetic behaviour.