Structural,magnetic and Mössbauer spectroscopic investigations of the magnetoelectric relaxor Pb(Fe0.6W0.2Nb0.2)O3

The complex perovskite lead iron tungsten niobium oxide, Pb(Fe_0.6W_0.2Nb_0.2)O₃ (PFWN) which belongs to the class of disordered magnetoelectrics, has been studied by X-ray and neutron powder diffraction, magnetic and Mössbauer spectroscopic measurements. Structural, dielectric and magnetic properties of PFWN are presented and reviewed. Magnetic measurements indicate that the most important interactions are of antiferromagnetic nature yielding T_N = 300 K, however, with indications of a reentrant spin glass behaviour below 20 K. The parameters of Mössbauer spectra also support the existence of the magnetic order and are consistent with the presence of high-spin Fe³⁺ cations located in the octahedral B-site. Rietveld refinements of diffraction data at different temperatures between 10 and 700 K have been carried out. The long-range structure of PFWN is cubic (space group Pm?3m) over the whole temperature interval. The Fe, W and Nb cations were found to be disordered over the perovskite B-sites. The Pb cations show a position disorder along the 〈111〉 direction shifting from their high-symmetry position. At the temperatures below T_N, an antiferromagnetic arrangement of the magnetic moments of Fe³⁺ cations in the B-site is proposed in accordance with the antiferromagnetic properties of PFWN. The factors governing the observed nuclear and magnetic structures of PFWN are discussed and compared with those of pure Pb(Fe_0.67W_0.33)O₃, Pb(Fe_0.5Nb_0.5)O₃ and other quaternary Pb-based perovskites containing iron.