Mossbauer study of amorphous Fe73.5Cu1Nb3Si13.5B9 alloy

This paper reports a Mossbauer study of amorphous Fe73.5Cu1Nb3Si13.5B9 alloy between 10 and 673 K. The Curie temperature T-C is found to be 620 +/- 1 K. The temperature dependence of the reduced average hyperfine field can be explained on the basis of Handrich's model of amorphous ferromagnetism, in which the parameter delta, which measures fluctuations in the exchange interactions, is assumed to have a temperature dependence delta = 0.525 + 0.208t - 0.55lt(2), where t is T/T-C. At low temperatures, the average hyperfine field H-eff(T) can be fitted to H-eff(0)(1 - b(3/2)(T/T-C)(3/2)), with H-eff(0) = 255 +/- 1 kOe and b(3/2) = 0.43 over a large temperature range (T/T-C < 0.5), which indicates the presence of long-wavelength spin-wave excitations in the amorphous alloy. At temperatures below T-C, the reduced average hyperfine field varies as D(1 - T/T-C)(beta), with D = 1.08 +/- 0.03 and beta = 0.36 +/- 0.03 over a large temperature range (1 > T/T-C > 0.4). Above the Curie temperature T-C, an average quadrupole splitting value of about 0.44 mm/s is found. The temperature dependence of the isomer shift can be fitted within the harmonic approximation to a Debye model with a Debye temperature Theta(D) = 355.6 K.