Abstract
A lot of progress has been made these last years about the understanding of colossal magnetoresistance (CMR) properties of manganites with the perovskite structure. The role of the interpolated cation (size, mismatch effect) is now well established, whereas the mixed valency of manganese Mn(III)–Mn(IV) is primordial for the appearance of this phenomenon which originates from double exchange between Mn3+ and Mn4+ species. The present paper is focused on the possibility to introduce other elements on the Mn-sites of the perovskite to enhance their CMR properties. The doping of manganites with various elements (Al, Ga, In, Ti, Sn, Fe, Cr, Co, Ni, Mg) is first reviewed. This study allows some spectacular effects to be evidenced for several perovskites (increase of TC and of CMR effect by several orders of magnitude, induced CMR effects in insulating perovskites). Clearly, the doping of the Mn-sites modifies dramatically the magnetic phase diagrams established on the only basis of the size effect by different authors. The second point deals with the synthesis of new magnetoresistant oxides without manganese: the 112-type cobaltites LnBaCo2O5.4 (Ln=Eu, Gd) which are oxygen deficient perovskites and the 1201-type oxide Tl0.94Sr2Cu0.4Co0.6O5−δ whose magnetotransport properties are studied.
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