Effect of Monovalent Doping on the Structural, Magnetic and Magnetocaloric Properties in La0.7M0.2M ′ 0.1MnO3 Manganese Oxides (M=Sr, Ba and M ′ =Na, Ag, K)

AbstractStructural, magnetic and magnetocaloric effects of powder perovskite manganites La0.7M0.2M′0.1MnO3 (M=Sr, Ba and M′=Na, Ag and K) have been investigated. Our samples have been elaborated using the conventional solid state reaction at high temperature. X-Ray diffraction characterizations showed that all our synthesized samples crystallize in the distorted rhombohedral system with R3̄c space group. Magnetization measurements versus temperature in a magnetic applied field of 50 mT showed that all our samples are ferromagnetic above room temperature. From the measured magnetization data of our synthesized samples as a function of magnetic applied field, the associated magnetic entropy change close to their respective Curie temperature TC and the relative cooling power RCP have been determined. A maximum magnetic entropy change, |ΔSMMax|, of 4.07 Jkg−1 K around 345 K was obtained in La0.7Sr0.2Na0.1MnO3 sample upon a magnetic field change of 5 T. The |ΔSMMax| values of La0.7Ba0.2M′0.1MnO3 are smaller in magnitude compared to La0.7Sr0.2M′0.1MnO3 samples and occur at lower temperatures

Role of A-site deficiency in the magneto-transport properties of Pr0.7Sr0.3MnO3 relaxed films

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Role of A-site deficiency in the magneto-transport properties of Pr 0.7 Sr 0.3 MnO 3 relaxed films

The magneto-transport properties of thick relaxed A-site deficient films having the composition Pr $_{0.6}\square_{0.1}$ Sr 0.3 MnO 3 (P □ SMO with the □ symbol for the Pr vacancy) and Pr 0.7 Sr $_{0.2}\square_{0.1}$ MnO 3 (PS □ MO) are studied. A direct comparison with a Pr 0.7 Sr 0.3 MnO 3 (PSMO)completely relaxed film, deposited under the same growth conditions, shows a reduction of the in-plane parameter a 100 associated to an enhancement of the out-plane parameter. The strains (bulk strain ε B and biaxial Jahn-Teller strain ε J-T ) do vary with the nature of the cationic vacancy. For example, an enhancement of ε B of 9% in the PS □ MO film (Sr deficient) produces a decrease of T C of 30 K, whereas the Pr deficient P □ SMO film exhibits a large reduction of both ε B (-16%) and ε J-T (divided by a factor of 5), which enhances T C of 12 K, similarly to previous observations on bulk ceramics. With a reduced resistivity (ρ>0.02 Ω cm), the obtained Pr-deficient film, P □ SMO, exhibits the best magneto-transport properties with a decreasing magnetoresistance sensitivity at low field. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2005