Magnetic properties of NiAs-type Fe-Sb-Te alloys

The influence of the addition of Te on the physical and magnetic properties of the binary alloy Fe_0.540Sb_0.460 (i.e. Fe _l.173Sb) was studied using X-ray diffraction, Mössbauer spectroscopy and magnetic susceptibility measurements. The specimens are characterized as single NiAs-type phases and their lattice parameters are calculated. The temperature dependence of the hyperfine interaction parameters has shown that iron occupies two distinct crystallographic sites: FeI in octahedrally coordinated regular sites is ordered antiferromagnetically, while FeII occupies pyramidal interstitial positions and remains paramagnetic. The phase transition temperature of FeI is influenced by Fe and/or Te/Sb substitutions. The strength of the covalent bonding of the resonant atom to the lattice is described in terms of the Mössbauer temperature θ_M deduced from the temperature dependence of the area under the resonance curve. The findings are clearly correlated with the ionicity variations of the chemical bonds as indicated by the changes in the axial ratio c/a and the magnetic moments.