Giant magnetothermal anomalies and direct measurements of the magnetocaloric effect in Pr0.7Sr0.3_xBaxMnO3 manganites

Abstract

The paper presents the results of a study of magnetization, specific heat (CP), thermal diffusivity (1), thermal conductivity (x) and direct measurements magnetocaloric effect of polycrystalline samples Pr0.7Sr0.3_xBaxMnO3 (x = 0-0.3). An increase in the Ba concentration leads to a decrease in the Curie temperature (TC), an increase in the disorder parameter (02) and a noticeable increase in thermal conductivity of the ferromagnetic phase (FM). The & kappa;(T) data near Tc revealed small minima and a sharp jump-like change in thermal conductivity upon transition to the FM phase. These results suggest that the anomalies in the temperature dependences of & eta;(T) and & kappa;(T) are associated with the scattering of thermal phonons both from distortions of the crystal lattice and from spin fluctuations. The giant change of & eta; (& UDelta;& eta;/& eta; -67%) and & kappa; (& UDelta;& kappa;/& kappa; -33%) was found in a magnetic field of 1.8 T for the x = 0 (Pr0.7Sr0.3MnO3) sample. The maximum values of & UDelta;T, & UDelta;S and relative cooling power (RCP), observed for this sample in a field of 1.8 T, are equal to 1.81 K, 3.38 J/kg K and 74.02 J/kg, respectively. In the studied Pr0.7Sr0.3_ xBaxMnO3 samples, the specific cooling power value at f = 0.2 Hz is 0.35, 0.29, 0.21, and 0.11 W/g for x = 0, 0.1, 0.2, and 0.3 sample, respectively.