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

The zero-field splitting parameter D of the 6 S 5/2 ground state of Mn 2+ 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 Mn 2+ ions in a representative group of six chloride host compounds: CdCl 2 , MgCl 2 , CsMgCl 3 , CsZnCl 5 , TMCC and (CH 2 NH 3 ) 2 CdCl 4 . In contrast, the empirical superposition model gives a consistent account of the experimental data for six-fold coordinated Mn 2+ ions in this group of compounds. The dependence of the intrinsic parameter b 2 on ligand distance R is found to be b 2 =-0.235 (R-R 0 ) cm -1 , with R 0 =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 (CH 3 NH 3 ) 2 MnCl 4 respectively.