Among the perovskite manganites, a series of La_1-xCa_xMnO₃ has the largest magneto-caloric effect (MCE) (|ΔS_m|_max=3.2-6.7 J/kg K at ΔH=13.5 kOe), but the Curie temperatures, T_C, are quite low (165-270 K). The system of LaSrMnO₃ has quite high T_C but its MCE is not so large. The manganites La_0.7(Ca_1-xSr_x)_0.3MnO₃ (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 ΔH=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. © 2009 Elsevier B.V. All rights reserved.

Islam M.S., Hanh D.T., Khan F.A., Hakim M.A., Minh D.L., Hoang N.N., Hai N.H., Chau N.

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Từ khóa : Cluster glass; High-T; Isothermal magnetization; Lattice parameters; Low field; Low temperatures; Magnetic refrigeration; Magneto-caloric effect; Magneto-caloric effects; Orthorhombic structures; Perovskite manganites; Room temperature; Single phase; Solid-state reaction techniques; Spin-glass behavior; Thermomagnetic measurement; Unit cells; Zero-field-cooled; Calcium; Cell membranes; Curie temperature; Glass; Lanthanum; Magnetic fields; Magnetos; Magnets; Manganites; Oxide minerals; Perovskite; Solid state reactions; Spin dynamics; Spin glass; Thermal effects