Effect of micro structure on magnetization processes in nanocrystalline Fe-Zr-B alloys

The nanocrystalline alloys produced by devitrification of the Fe89Zr7B4 amorphous alloy exhibit paramagnetic behaviour for the fractions of the crystalline phase lower than 13%. This is due to dendritic growth of crystals and paramagnetic properties of the amorphous matrix. A rapid increase of the nanocrystalline phase was observed for the 1 h annealings at temperatures between 480 and 540 °C. A formation of regular nanocrystals with diameters of about 50 nm and the increase of the Curie temperature of the amorphous matrix were accompanied by transition from para- to ferromagnetic properties. These properties were characterized by increasing saturation magnetization, magnetic permeability and Barkhausen noise intensity and decreasing coercivity of the alloy. Both the microstructure and magnetic properties vary only slightly for higher crystalline fractions up to 87%.