Electron paramagnetic resonance investigation of Fe 3C doped TlInS 2 single crystal F.A. Mikailov a,b, * , B.Z. Rameev a,c , S. Kazan a , F. Yıldız a , B. Aktas ¸ a a Department of Physics, Gebze Institute of Technology, 41400 Gebze, Kocaeli, Turkey b Institute of Physics, Azerbaijan Academy of Sciences, 370143 Baku, Azerbaijan c Kazan Physical-Technical Institute, 10/7, Sibirsky Trakt, 420029 Kazan, Russian Federation Received 25 January 2005; received in revised form 15 March 2005; accepted 21 March 2005 by C. Lacroix Available online 8 April 2005 Abstract TlInS 2 single crystal doped by paramagnetic Fe ions has been studied at room temperature by electron paramagnetic resonance (EPR) technique. The fine structure of EPR spectra of the paramagnetic Fe 3C ions is observed. The spectra were interpreted to correspond to the transitions among the spin multiplets (SZ5/2, LZ0) of the Fe 3C ion, which are split in the local ligand crystal field (CF) of orthorhombic symmetry. Four equivalent Fe 3C centers have been observed in the EPR spectra and the local symmetry of CF at the Fe 3C site and the CF parameters were determined. It was established that the symmetry axis of the axial component in the CF is making an angle of about 488 with the plane of layers of TlInS 2 crystal. Experimental results indicate that Fe ions substitute for In ions at the center of the InS 4 tetrahedrons, and the rhombic distortion of the CF is caused by Tl ions located in the trigonal cavities between the tetrahedral complexes. q 2005 Elsevier Ltd. All rights reserved. PACS: 75.10.Dg; 76.30.Da; 76.30.Kv; 71.70.Ch Keywords: D. Electron paramagnetic resonance; D. Fine structure splitting; D. Crystal field 1. Introduction The ternary compound TlInS 2 belongs to a group of ternary layered semiconductors with space group symmetry C 6 2h at room temperature [1]. According to X-ray diffraction measurements [2], the crystal structure of TlInS 2 consists of alternating two-dimensional metal-chalcogen layers. The layers are composed of In 4 S 10 tetrahedral complexes, which represent a combination of four elementary InS 4 tetrahedra and are linked together by common chalcogen atoms at the corners (Fig. 1). The elementary unit cell contains two partially disordered layers, containing successive rows of the tetrahedral complexes, which are turned away from each other by 908. Monovalent Tl atoms are in trigonal prismatic cavities resulting from the combination of the In 4 S 10 tetrahedra into a layer. As one can see in the figure, each successive layer is shifted along the [010] direction by the length of the edge of the small InS 4 tetrahedron with respect to the upper layer. As a result, a deviation from the tetragonal symmetry appears. The angle between the monoclinic c axis and the layer plane is about 1008. About two decades have passed, since, the first publication about the presence of structural phase transitions in ternary layered chalcogenide crystal TlInS 2 [3]. Since, that time this compound is investigated by using a great number of experimental methods. It has been established that TlInS 2 exhibits a sequence of structural phase transitions, including transitions to an incommensurate Solid State Communications 135 (2005) 114–118 www.elsevier.com/locate/ssc 0038-1098/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.ssc.2005.03.043 * Corresponding author. Address: Department of Physics, Gebze Institute of Technology, 41400 Gebze, Kocaeli, Turkey. Tel.: C90 262 6538497x1318; fax: C90 262 6538490. E-mail address: faik@gyte.edu.tr (F.A. Mikailov).