Hyperfine interactions and magnetization of (Fe1−xCox)80B20 amorphous alloys

Abstract

Mössbauer spectra of ternary (Fe1−xCox)80B20 ferromagnetic amorphous alloys were taken at 300, 77, and 6 K. The relatively broad distributions of the Fe57 hyperfine field could be fitted to quasi-symmetrical Gauss profiles with a relative half-intensity line width of 8–10%. Whereas the average hyperfine field HF at 6 K decreases slowly with x for x≳0.1, the isomer shift increases with x stronger than in the case of (Fe1−xNix)80B20 amorphous alloys. The saturation magnetization Ms has been measured in the temperature range 4–300 K. A linear dependence of HF (at 6 K) on the average magnetic moment μ holds over the whole investigated compositional range according to the equation HF = aμFe+μb where μFe is the moment of Fe in Fe80B20, a≃134 kOe/μB and b≃10 kOe/μB. A small enhancement of HF takes place only in the range 0<x<0.2 as does the average magnetic moment, but for both HF and μ the changes are much smaller than the crystalline FeCo alloys. The dependence of Ms on T is in very good agreement with the Bloch law Ms(T) = Ms(0)×[1−BT3/2] with values of B ranging between 0.67 and 1.25×10−5K3/2 for 0.75≳x≳0.125 in good agreement with those obtained from the dependence of HF on T.