Large reversible magnetocaloric effect in La0.7-xPr xCa0.3MnO3

Abstract

We report magnetocaloric effect in polycrystalline La 0.7-xPrxCa0.3MnO3 (x 0.0, 0.25, 0.3, 0.35, 0.4, and 0.45) samples. The magnetic entropy change (ΔS m) was measured using a differential scanning calorimeter (DSC) working in a magnetic field environment. The ΔSm shows a peak around the ferromagnetic Curie temperature (TC), and the magnitude of the peak decreases with increasing x (ΔSm 8.15, 7.27, 6.92, 6.73, 6.41, and 5.84 Jkg-1K-1 for x 0, 0.25, 0.3, 0.35, 0.4, and 0.45, respectively, for a field change of ΔH 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 ΔSm -7.09 Jkg-1K -1 at T 190 K and a relative cooling power of 306.5 Jkg-1 for H 5 T in x 0.35. We suggest that nanometer sized ferromagnetic clusters are pre-formed in the PM state above TC, 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 ΔSm values over a wide composition makes this series interesting for magnetic refrigeration in the temperature range T 100 K-270 K. © 2011 American Institute of Physics.