93Nb NMR and Fe3+ EPR study of local magnetic properties of magnetoelectric Pb(Fe1/2Nb1/2)O3

The 93Nb NMR and Fe3+ EPR spectra of a magnetoelectric Pb(Fe1/2Nb1/2)O3 (PFN) single crystal as well as of PFN ceramics and nanopowder have been measured. The relation between the chemical disorder and the local magnetic structure has been determined. The data show the occurrence of an antiferromagnetic (AFM) phase transition at 145 and 135 K in both single crystal and ceramic samples, respectively. The AFM phase transition is however essentially smeared out in the nanopowder. Two different Nb sites exist which have different local magnetic fields which are essentialy distributed in value. These two Nb sites correspond to different types of “chemical” order: Fe rich, Nb poor and Fe poor, Nb rich regions. The temperature dependences of the sublattice magnetizations and the values of the superhyperfine fields at the Nb ions are obtained. NMR data suggest that a spin–glass like state of PFN below T = 20 K arises from the Fe poor, Nb rich regions.