Effect of minor Cu addition on phase evolution and magnetic properties of {[(Fe_0.5Co_0.5)_0.75Si_0.05B_0.20]_0.96Nb_0.04}_100-x Cu_x alloys

{[(Fe_0.5Co_0.5)_0.75Si_0.05B_0.20]_0.96Nb_0.04}_100-xCu_x (x = 0, 1, 1.5 and 2) alloys with different rapid solidification conditions were prepared by copper mold casting and melt spinning. The structures, the thermal and the magnetic properties were studied by X-ray diffraction, differential scanning calorimetry and vibrating sample magnetometry, respectively. Minor Cu addition obviously depresses the glass-forming ability of the alloys (critical glassy diameter d_c < 1 mm) compared with [(Fe_0.5Co_0.5)_0.75Si_0.05B_0.20]₉₆ Nb⁴ (d_c = 3 mm). The effect of Cu addition on the evolution of crystalline phases corresponding to different rapid solidification conditions was evaluated. The existence of (Fe,Co), (Fe,Co)₃B, (Fe,Co)₂B and (Fe,Co)₂₃B₆ crystalline phases in {[(Fe_0.5Co_0.5)_0.75Si_0.05B_0.20]_0.96 Nb_0.04}_100-x Cu_x alloys influences the saturation magnetization compared with the corresponding glassy alloys.