A theoretical study on the temperature dependence of zero-field splitting for the tetragonal Cr3+ center in MgO crystal.

This paper reports a detailed theoretical calculation of the temperature dependence of zero-field splitting D (characterized by ΔD(T)=D(T)-D(0)) for the tetragonal Cr3+ center in MgO crystal by considering both the static contribution due to the thermal expansion of Cr3+ center and the vibrational contribution caused by electron-phonon (including the acoustic and optical phonons) interaction. The vibrational contribution due to the acoustic phonon is calculated using the long-wave approximation similar to the study on the specific heat of crystals and that due to optical phonon is estimated using the single-phonon model. The calculated results are in reasonable agreement with the experimental values.

Spin-Hamiltonian parameters and local structures for Co4+ and Ir4+ impurity centers in the tetragonal phase of SrTiO3.

The calculated results in the recent paper about the spin-Hamiltonian (SH) parameters (g factors g (//), g perpendicular and hyperfine structure constants A(//), A perpendicular) and the local structures of Co4+ and Ir4+ impurity centers in the tetragonal phase of SrTiO3 are doubtful because there are several mistakes in the calculations. So, we restudy the SH parameters and local structures by using the correct methods and parameters. From the studies, for Co4+ and Ir4+ in SrTiO3, the SH parameters are explained rationally, the signs of hyperfine structure constants A(//), A perpendicular are obtained and the suitable and more detailed local structures are given.