Crystallization and Mossbauer studies of the Fe78Al4Nb5B12Cu1 alloy

A melt-spun Fe78Al4Nb5B12Cu1 alloy with an ultra-thin ribbon has been studied by X-ray diffraction, Mossbauer spectroscopy, and vibrating sample magnetometry. The average hyperfine field H-hf(T) of the amorphous state shows a temperature dependence of [H-hf(T) - H-hf(0)]/H-hf(0) = -0.53(T/T-C)(3/2) - 0.21(T/T-C)(5/2) for T/T-C < 0.7, indicative of spin-wave excitation. The quadrupole splitting just above the Curie temperature Te is 0.42 mm/s, whereas the quadrupole shift below T-C is zero. The Curie and the crystallization temperatures are T-C = 450 K and T-x = 703 K, respectively, for a heating rate of 5 K/min. The occupied area ratio of the alpha-Fe phase flash-annealed at 723 K is 59% and remains unchanged. The crystallization temperature of the flash-annealed alloy becomes lower, and the formation of an alpha-Fe is easier than that of the conventional alloy. The flash-annealing technique is effective in improving the high-frequency soft magnetic property of the nanocrystalline Fe78Al4Nb5B12Cu1 alloy.