A research on the g factors and defect model for the tetragonal Sm3+ center in KMgF3 crystal

The g factors g and g⊥ for the tetragonal (SmF12)9− cluster due to Sm3+ occupying the 12-fold coordinated K+ site in KMgF3 perovskite are calculated from a diagonalization (of energy matrix) method. In the energy matrix, the crystal field parameters Bkq used are calculated from the superposition model with the intrinsic parameters A¯k(R0) close to those of (GdF12)9− clusters for Gd3+ in similar cubic perovskite c-RbZnF3. In the calculations, the applied defect model of tetragonal Sm3+ center in KMgF3 is that in which Sm3+ occupies the 12-fold coordinated K+ site associated with one (model A) or two (model B, where two K+ vacancies are at both sides of Sm3+) nearest K+ vacancies along the C4 axis for partial or complete charge compensation. The calculation results reveal that when the calculated g and g⊥ are in reasonable agreement with the experimental values, the tetragonal distortions of Sm3+ centers are, whether in model A or model B, very small because of the slight anisotropy of the observed g factors. So, we suggest that the defect model of Sm3+ center is that in which Sm3+ occupies the 12-fold coordinated K+ site associated with one or two next-nearest rather than nearest K+ vacancies along the C4 axis to result in small tetragonal distortions and hence in the small anisotropy of g factors. The reasonableness of our suggested defect model is discussed.