Orthorhombic standardization of spin-Hamiltonian parameters for transition-metal centres in various crystals

Several sets of non-standard zero-field splitting (ZFS) parameters in the spin Hamiltonian (SH) for transition-metal ions at orthorhombic or lower symmetry sites in various crystals have been revealed by a recent literature survey. The standardization limits the ratio of the orthorhombic ZFS parameters: (conventional) and (the extended Stevens (ES) notation). Based on the superposition model it is shown that the `maximum rhombicity' limit is valid not only in the effective SH sense but also in the crystallographic sense. Using the computer package CST the non-standard orthorhombic ZFS parameter sets given originally in various parameter and operator notations, units and conventions for the axis systems are standardized and presented in a unified way in the ES notation and units of . This enables a direct comparison with the available data for similar ion/host systems. The standardization reveals several inconsistencies in interpretation of earlier EPR results.