Elevated temperature initial permeability study of Fe73.5Cu1Nb3Si13.5B9 alloy

The effect of annealing temperature on the temperature dependence of initial permeability of Fe73.5Cu1Nb3Si13.5B9 alloy has been investigated. It was found that for the amorphous alloy consisting of a single phase a sharp Hopkinson peak appears and the Curie temperature value in as-quenched state was detected to be around 318 °C, which can be increased by annealing at Ta ≤ 460 °C. During the first stages of the crystallization to a nanophase structure, a smooth peak was observed on the μi–T curve. However, the nanostructured alloy containing a dual phase, which has excellent soft magnetic properties, showed a long tail character. In addition, at Ta = 600 °C two magnetic Curie transitions were found to be around 264 and 584 °C, corresponding to residual amorphous and α-Fe(Si) nanocrystal phase, respectively. According to the change in the microstructure after annealing, the influences of the magnetic characteristic of residual amorphous matrix and the volume fraction of α-Fe(Si) nanocrystalline phase on the magnetic exchange coupling between nanosized grains and the temperature dependence of initial permeability were also discussed.