Structural and Magnetic Properties of ${\hbox{Fe}}_{100\hbox{-}{\rm x}}{\hbox{Si}}_{\rm x}$ ($0\le x \le 40$) Nanocrystalline Alloy Powders

The authors report the investigations of effects of milling and composition on the evolution of nanocrystalline microstructure and magnetic properties of Fe
_100-x
Si
_x
(0 ≤ x ≤ 40) alloy powders synthesized by high energy ball milling over a wide composition range. We have observed from X-ray diffraction that a nonequilibrium solid solution could be obtained up to 35 at.% Si within 100 h of milling. Although these powders have fine crystallites with size ranging around 9 nm, their coercivity is rather high, which depends strongly both on milling condition and composition. While saturation magnetization ( MS) decreases continuously, coercivity shows a nonlinear variation with Si substitution. The variations of MS and lattice constant with Si substitution show a good correlation between the structural and magnetic properties. Curie temperature of Fe-Si solid solution decreases gradually at a rate of 1.45 K/at.% Si with increasing Si content. The observed results are discussed based on fine crystallite size, development of internal strain and grain boundaries, and variations in effective magnetic anisotropy in the mechanically alloyed nanocrystalline Fe-Si powder.