MICROSCOPIC STUDY OF CR2+ ION IN THE QUASI-2D MIXED SYSTEM RB2MNXCR1-XCL4

The effective point symmetry around Cr2+ ion in the quasi-two-dimensional (2D) mixed system Rb2MnxCr1-xCl4 is D2h but it approximates closely to D4h. Possible energy-level schemes for Cr2+ ion in the D4h as well as D2h 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 Rb2MnxCr1-xCl4. Using our earlier microscopic relationships between the spin Hamiltonian parameters b(k)q, g(i) and the energy level splittings (DELTA(i)) within the 5D term for D4h and D2h symmetry, values of b2(0), b2(2), b4(0), b4(2), b4(4) and g(x), g(y), g(z) are predicted for a wide range of the microscopic parameters involved. The diagrams of the parameters b2(0) and b2(2) versus the spin-orbit (lambda) and the spin-spin (rho) interaction parameters are worked out for a range of values of lambda and rho-specific for Cr2+. The dependence of the zero-field splitting parameters b(k)q on the concentration (x) in Rb2MnxCr1-xCl4 is also studied. Possible sources of the discrepancies between various experimental data for the parameters b2(0) and b2(2) are discussed. For the first time, the fourth-order parameters b4(0), b4(2) and b4(4) are determined. The present comprehensive investigation of the single-ion properties of Cr2+ ion in Rb2MnxCl1-xCl4 provides results indispensible for explaining the magnetic anisotropy as well as for predicting the EPR spectra at high frequency and high magnetic field.