Temperature Dependence of the Magnetization of an Amorphous Ferromagnet

An amorphous alloy ${\mathrm{Fe}}_{80}$ ${\mathrm{P}}_{12.5}$ ${\mathrm{C}}_{7.5}$ obtained by rapid quenching from the liquid state has previously been shown to be ferromagnetic. We report here the results of bulk magnetization and magnetic hyperfine field measurements as a function of temperature. The Mössbauer spectrum of the alloy consists of broadened lines indicating a nonunique magnetic hyperfine field at the ${\mathrm{Fe}}^{57}$ nuclei. The average hyperfine field has the value 282±1 kG at 4.2°K and is shown to vary with temperature essentially according to a Brillouin function with a Curie temperature of (586±2) °K. Measurements of the bulk magnetization as a function of temperature agree with the hyperfine field variation and yield a value for the magnetic moment per iron atom of $(2.10\mathrm{}\pm 0.01) {\mu }_B$. A simple model of a disordered alloy with a spread in interatomic spacing is used to predict the shape of the Mössbauer spectra and also to explain the reduction in magnetic moment per iron atom compared with pure iron. Although the magnetic moment per iron atom in this amorphous alloy is only slightly smaller than that of pure iron, the Curie temperature is greatly reduced, possibly because of the lack of strict periodicity in the atomic arrangement.