Magnetic, Magnetocaloric and Electric Transport Properties of Sr2FeMoO6-δ Double Perovskites with Different Degrees of Superstructural Ordering

Pressed strontium ferromolybdate (Sr2FeMoO6-δ) pellets with different oxygen indices d and degrees of superstructural ordering were synthesized by solid-phase and citrate-gel methods to study magnetic and electric transport behaviors of this compound. The crystalline structure of the samples was found to demonstrate ordering of the Fe and Mo cations, which increases with increase of δ. The saturation magnetization and the Curie temperature of the samples correlate with the degree of superstructural ordering. The Banerjee criterion indicates that the compounds studied undergo a second order phase transition. The temperature dependence of the isothermal change of entropy in magnetic field was determined by the Maxwell approach. The additional low-temperature annealing was found to change the sample conductivity of metallic type for semiconducting one and significantly increases magnetoresistance due to  the intergrain electron tunneling.