Structure and temperature dependence of magnetic properties in the nanocrystalline fe₇₄si_x;b_22-xcuinb₃ alloys

We have examined the structure and magnetic properties in terms of the temperature dependence of magnetic permeability and magnetization for the Fe₇₄Si_ZB_22-xCu₁Nb₃ (X = 8-18) alloys. The temperature dependence of the permeability of the alloys shows various characteristic behaviors depending on the alloy composition (x=8- 18) and annealing temperature (450-630°C). The permeability of the samples having coexisting a-Fe(Si) and amorphous phases decreases abruptly near the Curie temperature of the amorphous materials, while the permeability of the samples containing precipitated Fe-B compounds is not appreciably affected by the magnetism in the residual amorphous region. The precipitation of Fe-B compound depends on the composition of the mother alloys. The Fe-B compounds precipitated in the amorphous region upon annealing at high temperature are mainly Fe₂₃Be for X = 14, FegB for £ = 18, and Fe2B for the composition x less than 12.