Theoretical investigations of the microscopic spin Hamiltonian parameters including the spin-spin and spin-other-orbit interactions for Ni2+ (3d(8)) ions in trigonal crystal fields

摘要

The microscopic origin of the spin Hamiltonian (SH) parameters for Ni2+ (3d(8)) Zn ions in a trigonal type I symmetry (C-3v, D-3d, D-3) crystal field (CF) is studied. In addition to the spin-orbit (SO) interaction, we consider also the spin-spin (SS) and spin-other-orbit (SOO) interactions. The relative importance of the four (SO, SS, SOO, and combined SO-SS-SOO) contributions to the SH parameters is investigated using the CFA/MSH package and the complete diagonalization method (CDM). The SO mechanism is dominant for all CF parameter (CFP) ranges studied, except where the contributions D-SO to the zero-field splitting (ZFS) parameter D change sign. For the trigonal CFP, v(c) approximate to 1200 cm(-1) D due to the other three mechanisms exceeds D-SO. Although D-SOO is quite small, the combined DSO-SOO is appreciable. The SO-based perturbation theory (PT) works generally well for the g-factors: g() and g(perpendicular to), while it fails for D in the vicinity of v(c) and for large ' and v > 0. The high percentage discrepancy ratio delta(D) = 2020% for v(c) indicates unreliability of D-SO (in PT). Applications to Ni2+ ions at trigonal symmetry sites in LiNbO3, alpha-LiIO3, and Al2O3, are provided. The theoretical SH parameters are in good agreement with the experimental data. The low symmetry (C-3) effects induced by the angle p are tentatively studied, but appear to be quite small.