Synthesis and investigation of magneto-dielectric effect in A2FeMn0.5W0.5O6 (A = Ca, Sr, Ba) double perovskites

New perovskite oxides of the formula A2FeMn0.5W0.5O6 (A = Ca, Sr and Ba) have been prepared and their structure, magnetic, dielectric properties have been investigated. Ca2FeMn0.5W0.5O6 and Sr2FeMn0.5W0.5O6 compounds crystallize in cubic double perovskite structure (space group Fm-3m) whereas Ba2FeMn0.5W0.5O6 adopts the hexagonal 6H-type perovskite structure (space group P63/mmc). Magnetic measurements indicate that compositions are weakly ferromagnetic with dominating antiferromagnetic interactions at low temperatures. The dielectric behavior of A2FeMn0.5W0.5O6 (A = Ca, Sr and Ba) compounds is similar to that of relaxor ferroelectrics exhibiting the frequency dependence with a broad maxima around 350 K. Under 1 T applied magnetic field, the Ca and Sr members show a change in dielectric behavior indicating coupling between their magnetic and dielectric properties, while the Ba member did not show such effect. Further, on introducing oxygen vacancies (δ ∼ 0.28), the Ba compound undergoes a structural transformation from hexagonal to cubic and this transformation is reversible. The oxygen deficient member Ba2FeMn0.5W0.5O5.72 exhibits a significant enhancement in its magnetic behavior compared to that of the oxygen stoichiometric parent composition, Ba2FeMn0.5W0.5O6.