Microscopic study of Cr 2+ ion in the quasi-2D mixed system Rb 2Mn xCr 1− xCl 4

Abstract

The effective point symmetry around Cr 2+ ion in the quasi-two-dimensional (2D) mixed system Rb 2Mn x Cr 1− x Cl 4 is D 2h but it approximates closely to D 4h. Possible energy-level schemes for Cr 2+ ion in the D 4h as well as D 2h symmetry are investigated using the superposition model in order to discriminate between the two energy-level schemes assigned previously to the ground states ∥ x 2− y 2〉 and ∥z 2〉. The superposition model enables also study of the dependence of the crystal-field parameters and the energy levels on the concentration ( x) in Rb 2Mn x Cr 1− x Cl 4. Using our earlier microscopic relationships between the spin Hamiltonian parameters b k q , g i and the energy level splittings (Δ i) within the 5D term for D 4h and D 2h symmetry, values of b 2 0, b 2 2, b 4 0, b 4 2, b 4 4 and g x, g y, g z are predicted for a wide range of the microscopic parameters involved. The diagrams of the parameters b 2 0 and b 2 2 versus the spin-orbit (λ) and the spin-spin (ϱ) interaction parameters are worked out for a range of values of λ and ϱ specific for Cr 2+. The dependence of the zero-field splitting parameters b k q on the concentration ( x) in Rb 2Mn x Cr 1− x Cl 4 is also studied. Possible sources of the discrepancies between various experimental data for the parameters b 2 0 and b 2 2 are discussed. For the first time, the fourth-order parameters b 4 0, b 4 2 and b 4 4 are determined. The present comprehensive investigation of the single-ion properties of Cr 2+ ion in Rb 2Mn x Cl 1− x Cl 4 provides results indispensible for explaining the magnetic anisotropy as well as for predicting the EPR spectra at high frequency and high magnetic field.