Hyperfine interactions and magnetic properties of amorphous Fe-Sb alloys

We present a systematic investigation of amorphous Feₓ{Sb}_{100{{-}}x}$ alloys fabricated over a wide composition range (3{≤}x{≤}80). For the Fe-rich samples, the concentration dependence of the isomer shift is compatible with the Miedeme--van der Woude model, while a large discrepancy is found in samples with Fe concentrations less than 50 at. %. This suggests that a new term characteristic of sp elements is necessary in that model. The electric quadrupole splittings have been studied. A particularly striking feature comes from the discovery that the quadrupole splitting of crystalline x-FeSb₂ is larger than that of its amorphous counterpart a-FeSb₂ by a factor of 3 at both 4.2 and 300 K. Such a difference in quadrupole splitting is the largest ever found in Fe--sp-element and Fe--transition-element amorphous alloys. The magnetic ordering temperatures of the Fe-Sb alloys have been determined. At x>60, samples exhibit mainly ferromagnetic ordering, while below x=60, spin-glass behavior has been observed. The effective magnetic hyperfine field Heff, and hence the effective magnetic moment, of the Fe-Sb alloys increase monotonically with Fe concentration at about x=47. The distributions of magnetic hyperfine field P(H) are also presented and discussed.