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

Abstract The electron paramagnetic resonance (EPR) measurements of PbMoO 4 single crystals doped with Co 2+ 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 Nd 3+ ions in PbMoO 4 . The analysis of the various characteristic features of the EPR spectra as well as our earlier optical absorption studies of Co 2+ :PbMoO 4 indicate that the Co 2+ ions are located at two crystallographically distinct complexes, denoted Co 2+ (α) and Co 2+ (β). The fictitious ‘spin’ S ′ = ½ has been assigned to the observed ground Kramers doublet state of each of the two Co 2+ complexes tentatively identified as located at the Mo sites in PbMoO 4 . The spin Hamiltonian parameters for Co 2+ ( S ′ = ½) ions in PbMoO 4 , including the components of the Zeeman and hyperfine structure tensors g ij and A ij , respectively, are experimentally determined for the first time. Comparison of our results with the values of g ij and A ij for Co 2+ 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 Co 2+ ions in PbMoO 4 will be considered in a subsequent paper.