Large magnetocaloric effect around room temperature in La0.7Ca0.3-x Pb x MnO3 perovskites

Among perovskite manganites, a series La1-x Ca x MnO3 has the largest magnetocaloric effect (MCE) (|ΔS m|max=3.2-6.7 J/kg K in ΔH=1.35 T) but their Curie temperatures, T C, are quite low (165-270 K). A system La1-x Pb x MnO3 has quite high T C (235-360 K) but exhibits not so large MCE (0.65-1.53 J/kg K). The manganites La0.7Ca0.3-x Pb x MnO3 (x=0.05, 0.10, 0.15, and 0.20) have been fabricated by solid-state reaction technique with the expectation that they could establish large MCE at room temperature region. The prepared samples are of single phase with orthorhombic structure. Lattice parameters as well as volume of unit cell are continuously increased with increasing x due to large Pb2+ ions substituted for smaller Ca2+ ions. There is spin-glass (or cluster glass)-like state occurring in studied samples. T C increases continuously from 270 K (for x=0.05) to 338 K (for x=0.20). Large MCE has been obtained in all samples and vertical bar ΔS m vertical barmax reached the highest value of 3.72 J/kg K (with magnetic field variation ΔH=1.35 T) for the sample x=0.05 and the studied samples could be considered as giant magnetocaloric materials working for magnetic refrigeration. The magnetoresistance of samples exhibited colossal value