Electron paramagnetic resonance (EPR) investigations of the local environment around Co2+ ions doped in PbMoO4 single crystals – Correlation with optical studies

• The EPR measurements of PbMoO4 doped with Co2+ ions (10–12 K) are reported.
• Co2+ ions are located at two crystallographically distinct sites: Co2+(α) and Co2+(β).
• Co2+ ions identified as located at the Mo sites in PbMoO4.
• The HS parameters are experimentally determined by the least square fittings of the EPR spectra for both Co2+ complexes.

The electron paramagnetic resonance (EPR) measurements of PbMoO4 single crystals doped with Co2+ ions (0.5 wt.%) carried out at temperature range 10–12 K are reported. The observed spectra reveal evidently two major groups of EPR spectra, each group consists of eight hyperfine structure components associated with the Co nuclear spin I = 7/2. Additionally, EPR spectra of the unintentional impurities have been observed, which have been assigned to Nd3+ ions in PbMoO4. The analysis of the various characteristic features of the EPR spectra as well as our earlier optical absorption studies of Co2+:PbMoO4 indicate that the Co2+ ions are located at two crystallographically distinct complexes, denoted Co2+(α) and Co2+(β). The fictitious ‘spin’ S′ = ½ has been assigned to the observed ground Kramers doublet state of each of the two Co2+ complexes tentatively identified as located at the Mo sites in PbMoO4. The spin Hamiltonian parameters for Co2+ (S′ = ½) ions in PbMoO4, including the components of the Zeeman and hyperfine structure tensors gij and Aij, respectively, are experimentally determined for the first time. Comparison of our results with the values of gij and Aij for Co2+ ions in other structurally similar compounds further strengthens this conclusion. Correlation of the present results with those obtained earlier from optical studies is discussed. Alternative assignments of the ground states and options for the origin of the ‘spin’ S′ = ½ for Co2+ ions in PbMoO4 will be considered in a subsequent paper.