EPR and superposition-model analysis of zero-field splitting parameters for Mn²⁺ doped in ZnNbOF₅.6(H₂O) and CoNbOF₅ .6(H₂O) single crystals

The electron paramagnetic resonance (EPR) and crystallographic data have been previously documented in literature for Mn²⁺ doped zinc pentafluorooxodiobate (V) hexahydrate ZnNbOF₅.6H₂O (CPH) and cobalt pentafluorooxonibotae (V) hexahydrate CoNbO₅ .6H₂ O single crystal. In this study, a theoretical investigation of these crystals has been conducted using the superposition model (SPM). The superposition model (SPM) distinguish the geometrical and physical properties that are essential in crystal field parameters. By employing a simple linear least square fit of parameters to intrinsic parameters, the zero field splitting parameters (ZFS) of Mn²⁺ in ZPH and CPH can be determined from crystal structure din the lattice. This observation suggests that Mn²⁺ effectively replace Zn²⁺ and Co²⁺. The SPM analysis, relying on the assumption of n no. of identical structure around host and guest ions, consider only the immediately coordinated ions. Close agreement between theoretical values of b2 0 is achieved by adopting a reference distance of R₀ = 0.22 nm. The exponent power law t₂ = 7 ± 1 and t₄ = 10 ± 1 are determined for Mn²⁺ surrounded by oxygen. The fine structure constants are indicative of the specific arrangement of ligands nearby all the impurity ions, with zero-field splitting parameters b⁰₂, b²₂, b⁰₄, b²₄ and b⁴₄ showing sensitivity in the case where Mn²⁺ ions are coordinated by oxygen in single crystals. The results obtained from the superposition model align well with the experimental findings, especially when accounting for local distortion around the Mn²⁺ ion at substitutional site in the host crystal. This paper aims to investigate the local distortion caused by substituting Mn²⁺ in the host crystal, exploring its potential impact on its magnetic properties. (author)