Microscopic study of Cr²⁺ ion in the quasi-2D mixed system Rb2MnxCr1-xCl4

Authors:

• Czesław Zygmunt Rudowicz,
• Yi-yang Zhou

Abstract

The effective point symmetry around Cr²⁺ ion in the quasi-two-dimensional (2D) mixed system Rb₂Mn_xCr_1-xCl₄ is D_2h but it approximates closely to D_4h. Possible energy-level schemes for Cr²⁺ 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 ∥x²-y²〉 and ∥z²〉. The superposition model enables also study of the dependence of the crystal-field parameters and the energy levels on the concentration (x) in Rb₂Mn_xCr_1-xCl₄. 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 b₂⁰, b₂², b₄⁰, b₄², b₄⁴ and g_x, g_y, g_z are predicted for a wide range of the microscopic parameters involved. The diagrams of the parameters b₂⁰ and b₂² versus the spin-orbit (λ) and the spin-spin (ρ{variant}) interaction parameters are worked out for a range of values of λ and ρ{variant} specific for Cr²⁺. The dependence of the zero-field splitting parameters b_k^q on the concentration (x) in Rb₂Mn_xCr_1-xCl₄ is also studied. Possible sources of the discrepancies between various experimental data for the parameters b₂⁰ and b₂² are discussed. For the first time, the fourth-order parameters b₄⁰, b₄² and b₄⁴ are determined. The present comprehensive investigation of the single-ion properties of Cr²⁺ ion in Rb₂Mn_xCl_1-xCl₄ provides results indispensible for explaining the magnetic anisotropy as well as for predicting the EPR spectra at high frequency and high magnetic field. © 1992.