Twinned EPR spectra of Fe3+ centers in ternary layered TlGaS2 crystal

TlGaS2 single crystal doped by paramagnetic Fe3+ ions has been studied by electron paramagnetic resonance (EPR) technique. The fine structure of EPR spectra of paramagnetic Fe3+ ions was observed. The spectra reveal a nearly orthorhombic symmetry of the crystal field (CF) on the Fe3+ ions. Two groups each consisting of four equivalent Fe3+ centers were observed in the EPR spectra. The local symmetry of the crystal field on the Fe3+ centers and CF parameters were determined. Experimental results indicate that the Fe ions substitute Ga at the center of the GaS4 tetrahedrons. The rhombic distortion of the sulfur ligand CF is attributed to the effect of Tl ions located in the trigonal cavities between the tetrahedral complexes. The observed twinning of the resonance lines indicates a presence of two non-equivalent positions of Tl ions that confirms their zigzag alignment in the TlGaS2 crystal structure.