Large reversible magnetocaloric effect in La0.7-xPrxCa0.3MnO3

We report magnetocaloric effect in polycrystalline La0.7-xPrxCa0.3MnO3 (x = 0.0, 0.25, 0.3, 0.35, 0.4, and 0.45) samples. The magnetic entropy change (Delta S-m) was measured using a differential scanning calorimeter (DSC) working in a magnetic field environment. The Delta S-m shows a peak around the ferromagnetic Curie temperature (T-C), and the magnitude of the peak decreases with increasing x (Delta S-m = 8.15, 7.27, 6.92, 6.73, 6.41, and 5.84 Jkg(-1) K-1 for x = 0, 0.25, 0.3, 0.35, 0.4, and 0.45, respectively, for a field change of Delta H = 5 T). We have studied electrical, magnetoresistance, and magnetic properties of x = 0.35 compound in detail. The paramagnetic-ferromagnetic transition in this compound is found to be first order in nature. Magnetization isotherms show a field-induced metamagnetic transition in the paramagnetic (PM) state, and it is accompanied by a change in latent heat, as evidenced by the DSC data. Magnetization data give Delta S-m = -7.09 Jkg(-1) K-1 at T = 190 K and a relative cooling power of 306.5 Jkg(-1) for Delta H = 5 T in x = 0.35. We suggest that nanometer sized ferromagnetic clusters are pre-formed in the PM state above T-C, and they coexist with short-range charge-orbital-ordered (COO) clusters in zero H field for x > 0. The observed large magnetocaloric effect with negligible hysteresis in M-H is associated with the metamagnetic transition resulting from the destruction of the COO clusters and growth of ferromagnetic clusters in size. The existence of significant Delta Sm values over a wide composition makes this series interesting for magnetic refrigeration in the temperature range T = 100 K-270 K. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3603014]