Giant magneto-caloric effect around room temperature at moderate low field variation in La0.7(Ca1-xSrx)0.3MnO3 perovskites

Among the perovskite manganites, a series of La1-xCaxMnO3 has the largest magneto-caloric effect (MCE) (vertical bar Delta S-m vertical bar(max) = 3.2-6.7 J/kg K at Delta H = 13.5 kOe), but the Curie temperatures, T-C, are quite low (165-270K). The system of LaSrMnO3 has quite high T-C but its MCE is not so large. The manganites La-0.7(Ca1-xSrx)(0.3)MnO3 (x = 0, 0.05, 0.10, 0.15, 0.20, 0.25) have been prepared by solid state reaction technique with an expectation of large MCE at room temperature region. The samples are of single phase with orthorhombic structure. The lattice parameters as well as the volume of unit cell are continuously increased with the increase of x due to large Sr2+ ions substituted for smaller Ca2+ ions. The field-cooled (FC) and zero-field-cooled (ZFC) thermomagnetic measurements at low field and low temperatures indicate that there is a spin-glass like (or cluster glass) state occurred. The Curie temperature T-C increases continuously from 258 K (for x = 0) to 293 K (for x = 0.25). A large MCE of 5 J/kg K has been observed around 293 K at the magnetic field change Delta H = 13.5 kOe for the sample x = 0.25. The studied samples can be considered as giant magneto-caloric materials, which is an excellent candidate for magnetic refrigeration at room temperature region. (C) 2009 Elsevier B.V. All rights reserved.