Giant magnetothermal anomalies and direct measurements of the magnetocaloric effect in Pr0.7Sr0.3−xBaxMnO3 manganites

The paper presents the results of a study of magnetization, specific heat (CP), thermal diffusivity (η), thermal conductivity (κ) 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 (σ2) and a noticeable increase in thermal conductivity of the ferromagnetic phase (FM). The κ(Т) data near ТС 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 η(Т) and κ(Т) are associated with the scattering of thermal phonons both from distortions of the crystal lattice and from spin fluctuations. The giant change of η (Δη/η ∼ 67%) and κ (Δκ/κ ∼ 33%) was found in a magnetic field of 1.8 T for the x = 0 (Pr0.7Sr0.3MnO3) sample. The maximum values of ∆T, ∆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.