Journal of Magnetism and Magnetic Materials 292 (2005) 37–43 Magnetic properties of NiAs-type Fe–Sb–Te alloys A.M. Gismelseed à , A.A. Yousif Department of Physics, College of Science, Sultan Qaboos University College, Box 36, Code 123, Alkhond, Oman Received 2 July 2004; received in revised form 2 October 2004 Available online 10 November 2004 Abstract The influence of the addition of Te on the physical and magnetic properties of the binary alloy Fe 0.540 Sb 0.460 (i.e. Fe l.173 Sb) was studied using X-ray diffraction, Mo¨ ssbauer 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 Mo¨ssbauer temperature y 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. r 2004 Elsevier B.V. All rights reserved. PACS: 75.50.Bb; 75.50.Ee; 76.80.+y Keywords: Mo¨ssbauer of FeSbTe; Ternary alloys; Magnetic properties; Lattice dynamics 1. Introduction Due to the formation of different crystallo- graphic structures, the transition-metal chalcogen- ides show many interesting magnetic and optical properties. The alloys FeSb 2 and FeTe 2 that are characterized by the marcasite structure exhibit paramagnetic properties down to 4.2 K [1]. How- ever, the ternary alloys Fe(Sb 1x Te x ) 2 are mag- netic below 70 K when Te substitutes Sb within the range 0pxp0.3, while remaining paramagnetic down to 4.2K at higher Te concentration. The observed magnetic behavior has been attributed to the reduction of the existing energy gap in the FeSb 2 system by the addition of Te anions [2,3]. On the other hand, the binary alloys iron-rich Fe l+x Sb and iron-deficient Fe 1x Te have been structurally investigated as B8-type (NiAs-type), ARTICLE IN PRESS www.elsevier.com/locate/jmmm 0304-8853/$-see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2004.10.092 à Corresponding author. Tel.: +009689811092; fax: +00968514228. E-mail address: abbasher@squ.edu.om (A.M. Gismelseed).