Defect model and spin-Hamiltonian parameters for the tetragonal Nd 3+ center in the tetragonal phase of SrTiO 3 crystal

Abstract

The spin-Hamiltonian parameters ( g factors g ∥, g ⊥ and hyperfine structure constants 143A ∥, 143A ⊥, 145A ∥ and 145A ⊥) of the tetragonal Nd 3+ center in the low-temperature ( T≈4.2 K) tetragonal phase of SrTiO 3 are calculated from a diagonalization (of energy matrix) method. In the method, the Zeeman and hyperfine interaction terms are attached to the conventional Hamiltonian and a 52×52 energy matrix concerning the ground term 4 H J ( J=9/2, 11/2, 13/2, 15/2) is constructed. The Nd 3+ center is attributed to Nd 3+ occupying the 12-fold coordinated Sr 2+ site in SrTiO 3. Differing from the defect model assumed in the previous paper that the tetragonal distortion of this Nd 3+ center is due to the association of one interstitial oxygen ion at a nearest neighborhood of Nd 3+ and the Nd 3+ displacement Δ z along C 4 axis, we suggest that it is due to the distortion of SrTiO 3 lattice in the tetragonal phase. The calculated g factors g ∥ and g ⊥ show good agreement with the experimental values, suggesting that our defect model of Nd 3+ center in SrTiO 3 is reasonable. The experimental hyperfine structure constants were not reported and so our calculated results remain to be checked by EPR experiment.