Structural and magnetic properties of amorphous and nanocrystalline Fe–Si–B–P–Nb–Cu alloys produced by gas atomization

Fe–Si–B–Nb–Cu alloy powders, with and without P additions, were produced by gas atomization. The particles smaller than 20 μm are fully amorphous, exhibiting good soft magnetic properties. The crystallization process was studied by differential scanning calorimetry, demonstrating that its kinetics changes dramatically with small variations in the composition. The (Fe_0.76Si_0.09B_0.10P_0.05)_97.5Nb_2.0Cu_0.5 (at. %) alloy was annealed in the supercooled liquid region (480 °C) and at the first crystallization peak (530 °C). The structural characterization by means of differential scanning calorimetry, X-ray diffraction, and transmission electron microscopy provided information that explained the excellent soft magnetic properties. Annealing at 480 °C produced an amorphous relaxed structure with improved soft magnetic properties. At 530 °C, a two-phase material formed by nanocrystals with an average grain size of 16–17 nm embedded in an amorphous matrix was developed. Partial nanocrystallization increased the saturation magnetization from 139 to 144 emu/g and reduced the coercivity from 2.24 to 0.69 Oe. These results can be understood in terms of the algebraic contribution of both phases to the magnetization and the application of the random anisotropy model to nanocrystalline soft magnetic materials.