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      Articles written in Bulletin of Materials Science

    • Effect of Co substitution on the physicochemical properties of La$_{0.67}$Sr$_{0.22}$Ba$_{0.11}$Mn$_{1−x}$Co$_x$O$_3$ compounds ($0 \le x \le 0.3$)

      W CHERIF R BEN HASSINE J A ALONSO F J MOMPEÁN M T FERNÁNDEZ-DÍAZ F ELHALOUANI

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      We have prepared a novel series of La$_{0.67}$Sr$_{0.22}$Ba$_{0.11}$Mn$_{1−x}$Co$_x$O$_3$ ($0 \le x \le 0.3$) perovskites by a sol–gel method. These oxides were characterized by X-ray diffraction (XRD) and neutron powder diffraction (NPD) at room temperature and magnetization measurements vs. temperature and various applied magnetic fields. The use of NPD data allows us to describe very precisely the octahedral tilting in the orthorhombic structure (Pnma) observed for all the compounds ($x = 0$ to 0.3); in all the samples with $x > 0$, Co is distributed at random in theMn positions of the perovskite. Magnetic susceptibility measurements show that whereas the $x = 0$ perovskite is ferromagnetic at relatively high temperatures ($T_C = 360$ K), the introduction of Co induces a magnetic glass state(cluster or spin glass). The magnetic entropy change ($|\Delta S^{\max}|$) takes values 2.46, 2.43, 1.88 and 1.78 J kg$^{−1}$ K$^{−1}$ for $x = 0$, 0.1, 0.2 and 0.3, respectively. The relative cooling power is 169, 241, 207 and 191 J kg$^{−1}$ for $x = 0$, 0.1, 0.2 and 0.3, respectively, at a field change of 5T. This result suggests that subtle Co doping enhances the magnetocaloric effect in this series, the perovskite La$_{0.67}$Sr${_{0.22}$Ba$_{0.11}$Mn$_{0.9}$Co$_{0.1}$O$_3$ being a candidate that can be used in magnetic refrigeration.

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