Magnetic single-ion anisotropy and zero-field splittings of Mn2+ions in some low-dimensional chlorides

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Abstract
The zero-field splitting parameter D of the 6S5/2 ground state of Mn2+ ions with Cl- ligands is discussed. Ab initio calculations of D, based on the relativistic spin-spin and Blume-Orbach splitting mechanisms, and an electrostatic model of the crystal field, are in poor agreement with experimental measurements for Mn2+ ions in a representative group of six chloride host compounds: CdCl2, MgCl2, CsMgCl3, CsZnCl5, TMCC and (CH2NH3)2CdCl4. In contrast, the empirical superposition model gives a consistent account of the experimental data for six-fold coordinated Mn2+ ions in this group of compounds. The dependence of the intrinsic parameter b2 on ligand distance R is found to be b2=-0.235 (R-R0) cm-1, with R0=2.692 AA, suggesting that the zero-field splitting involves a cancellation effect between two competing mechanisms. The superposition model is used to predict zero-field splittings of D=+0.019 and +0.036 cm-1 in the low-dimensional antiferromagnets TMMC and (CH3NH3)2 MnCl4 respectively.