EPR and optical study of Mn doped ammonium oxalate monohydrate

Studies on fine and hyperfine structures of paramagnetic resonance spectra in single crystals of Mn²⁺: ammonium oxalate monohydrate are reported. As sufficient numbers of lines were not obtained at room temperature, measurements have been done at liquid nitrogen temperature and at the frequency of X-band. The Mn²⁺ spin Hamiltonian parameters have been evaluated employing a large number of resonant line positions observed for various orientations of the external magnetic field and the surrounding crystalline field has been discussed. The values of the zero field parameters that give good fit to the observed EPR spectra have been evaluated. The values obtained for g, A, B, D, E and a are 2.0002±0.0002, (100±2)×10⁻⁴, (79.5±2)×10⁻⁴, (257±2)×10⁻⁴, (85±2)×10⁻⁴ and (−18±1)×10⁻⁴ cm⁻¹, respectively. The percentage of covalency of the metal-ligand bond is also determined. The optical absorption study has been done at room temperature. The observed bands are assigned as transitions from the ⁶A_1g(S) ground state to various excited quartet levels of Mn²⁺ ion in a cubic crystalline field. The electron repulsion parameters (B and C), the crystal field splitting parameter(Dq) and the Trees correction (α) providing good fit to the observed optical spectra have been estimated and the values obtained for the parameters are B=897, C=2144, Dq=910 and α=76 cm⁻¹.