Studies of the spin-Hamiltonian parameters and defect structures for Cu~(2+) ions in AgCl and NaCl crystals from a two-mechanism model

摘要

In this paper, based on a two-mechanism model, we derive the complete high-order perturbation formulas of the spin-Hamiltonian (SH) parameters (g factors g_∥, g_⊥ and hyperfine structure constants A_∥, A_⊥) for 3d~9 ions in tetragonally elongated octahedral clusters. In the model, the contributions to SH parameters due to the crystal-field (CF) mechanism related to CF excited states and the charge-transfer (CT) mechanism related to CT exacted states (the CT mechanism is neglected in CF theory, which is widely used to study the SH parameters) are taken into account. From these formulas, the SH parameters of Cu~(2+) ions in AgCl and NaCl crystals are calculated. It is found that for the exact explanation of SH parameters of (CuCl_6)~(4-) clusters in crystals, the contribution due to CT mechanism should be considered. The relative importance of CT mechanism (characterized by Q~(CT)/Q ~(CF), where Q = g_i or A_i~((2)), i = ∥ or ⊥) increases with the decreasing metal-ligand distance in (CuCl _6)~(4-) clusters. The causes are discussed. The signs of A_i and the defect structures of Cu~(2+) centers in AgCl and NaCl crystals are suggested from the calculations.