Structural, magnetic and thermodynamic properties of barium ferromolybdate

The heat capacity and magnetisation of the obtained by the solid-phase method from simple oxides single-phase compound Ba2FeMoO6-delta, in which the superstructural ordering of Fe and Mo cations occurs, was studied. The anomalous behaviour of the temperature dependences of heat capacity (deviation from Debye T-3 law) and magnetic moment (ZFC mode) is interpreted as the existence of a superparamagnetic state in nanoscale grains. The second lambda-type anomaly of heat capacity in the region of 300 K is due to the transition of the compound from the ferrimagnetic to the paramagnetic state. The Curie temperature, determined from the maximum of excess heat capacity in the region, is in good agreement with the Curie temperature obtained from the results of magnetic measurements, T-C = 302 K. Based on the Ba2FeMoO6-delta compounds heat capacity data the next thermodynamic functions were calculated: reduced enthalpy, entropy, reduced Gibbs energy. The values of calculated functions in the region of temperature anomalies made it possible to classify such anomalies as second-order phase transitions.