Electron paramagnetic resonance spectra of Fe''3''+ centers in TlGaSe2 crystal

The TlGaSe2 single crystal doped by paramagnetic Fe''3''+ ions has been studied by Electron Spin Resonance (ESR) technique. The crystals were grown by using a modified Bridgman method by taking initial ratio of Fe/Ga as 2%. The ESR spectra have been taken by using Bruker EMX series X-band spectrometer (9.5 GHz). The spectra were recorded at different orientations of DC magnetic field to study the crystal field symmetry around the impurity ion. TlGaSe2 belongs to a group of ternary layered semiconductors with a space group symmetry C2h''6 at room temperature. The crystal structure of TlGaSe2 is characterized by metal-chalcogen layers composed of Ga4Se10 complexes linked by common chalcogen atoms at the corners. Elemantary unit cell contains two layers, containing successive raws of the tetrahedron complexes which are turned away from each other by 90 #degree#. Each complex contains GaSe4 tetrahedrons. Monovalent Tl ions are located in the trigonal cavities between metal-chalcogen layers. It has been established that the ESR spectra originates from paramagnetic Fe''3''+ ion. The degeneracy of spin multiplet of S-state of Fe''3''+ ion (S=5/2, L=0) is removed due to the crystal field. ESR spectrum was shown to correspond to the transitions among spin multiplet of Fe''3''+ ion located at the center of the GaSe4 tetrahedron formed by Se atoms. The EPR spectra from Fe''3''+ centres can be described by the following spin-Hamiltonian: H=βB''→g''#->''->#S''#->3+1/3Σm=0''2b2''mO2''m+1/60Σm=0''4b4''mO4''m where the electronic spin S=5/2 and β is Bohr magneton. The first term accounts for the Zeeman interaction, the second term is the crystal-field Hamiltonian. The Stevens operators On''m are defined according to Abragam and Bleaney. Angular dependencies of resonance field values were established from EPR spectra. The values of spin-Hamiltonian parameters were extracted. The results were discussed with respect to the crystal structure of TlGaSe2 compound. The symmetry of crystal field (CF) at the Fe''3''+ site was determined. According to the results, the CF at the center of GaSe4 tetrahedron exhibits tetragonal distortion.