Crystal field levels and zero-field splitting parameters of Cr 2+ in the mixed system Rb2MnxCr1− xCl4

Abstract

The crystal field (CF) energy levels and the fine structure of the orbital ground state as well as the zero-field splitting (ZFS) parameters are investigated for Cr 2+ in the mixed system Rb 2 Mn x Cr 1− x Cl 4. The CF parameters from the earlier superposition model analysis are used as input for a newly developed computer package to diagonalize the orthorhombic CF and spin-orbit Hamiltonian for two cases, namely, the 5D approximation and the 5D- 3Γ i one. The results show that the spin-triplets ( 3Γ i ) contributions to the fine structure of the orbital ground state and the ZFS parameters are not negligible, although all 3Γ i states lie above the 5D states. The theoretical CF levels for different Cr 2+ concentrations ( x) are in good agreement with experimental spectroscopic data. For the axial ZFS parameter b 0 2, the theoretical result is consistent with the experimental magnetic anisotropy data. A change in the sign of the orthorhombic ZFS parameter b 2 2 with Cr 2+ concentration x increasing from x = 0 to x = 0.01 is predicted. This is consistent with the crystal structure data which indicate a ‘structural phase transition’ with x at low temperatures. EPR studies would help to solve the question of the sign of b 2 2 unambiguously.