Correlation between structure and magnetic behavior of Fe-P amorphous alloys

A series of Fe_100-x{P}ₓ$ alloys (x=11--22) have been prepared by electrodeposition. Fully amorphous samples (x=16--22) have been investigated from both a magnetic and a structural point of view, in order to clarify the magnetic behavior of such alloys. Magnetization, M\"ossbauer, and extended x-ray-absorption fine structure (EXAFS) measurements (in both the Fe-K and P-K edges) have been performed. The concentration dependence of the saturation magnetization at 0 K, the isomer shift, and the mean hyperfine field have been obtained using the first two techniques and agree with previously reported data. The structural parameters obtained by EXAFS spectroscopy indicate no change in the Fe-Fe nearest-neighbor arrangement in the series and only a slight increase in the number of P atoms around Fe as the P content increases. We observe a T² temperature dependence of magnetization, indicative of itinerant rather than localized magnetism. The atomic disorder of the samples is discussed in terms of the shape of the hyperfine field distributions and the structural disorder parameters obtained in the fit of the EXAFS spectra, and can be related to the behavior of the spontaneous magnetization. The characteristic behavior of the Curie temperature, whose value remains nearly unchanged over the range of composition studied, can be explained as a cancellation of volume effects and electron transfer from P to the 3d band of Fe.