EPR spectroscopy of the Cr3+ centers in LLGG:Cr single crystals

The X-band (ν congruent with 9.4 GHz) electron paramagnetic resonance (EPR) of series of Cr-doped lanthanum lutetium gallium garnet (LLGG) single crystals with various compositions and Cr concentrations were investigated at room and liquid nitrogen temperatures. All observed EPR spectra were assigned to Cr3+ ions (3d3 configuration, 4A2g ground state). Angular dependencies of the observed EPR spectra show three different types of Cr3+ centers in the octahedral sites of LLGG lattice: isolated Cr3+ centers of axial symmetry, isolated Cr3+ centers of rhombic symmetry, and magnetically coupled Cr3+ clusters (or clumps). The parameters of the Cr3+ centers of axial and rhombic symmetry were evaluated. The possible crystallographic models of the isolated Cr3+ centers and the influence of the substitutional disorder on the formation process of the different Cr3+ centers in the LLGG lattice are discussed