Competition between charge ordering and ferromagnetism in manganese perovskites
1997
Abstract Manganese perovskites have recently been the subject of renewed attention, due to the “colossal” magnetoresistance (CMR) and the coupled metal-insulator and magnetic transitions displayed at the spin-ordering temperature T C by some of these compounds. The charge localization mechanism above T c appears at present to be the single most important issue in manganite research. Neutron and synchrotron X-ray diffraction studies have revealed, for appropriate doping ranges, a strong competition between the metallic state, which is ferromagnetic and shows small lattice distortions, and a charge-localized/ordered state that becomes antiferromagnetic at low temperatures and shows large lattice distortions of the Jahn-Teller type. In the case of La 0.5 Ca 0.5 MnO 3 and Pr 0.7 Ca 0.3 MnO 3 , these two states can coexist giving rise to transient inhomogeneities. The possibility that a similar situation may be reproduced in the paramagnetic phase will be discussed, in the light of recent neutron-diffuse-scattering data suggestive of extended ferromagnetic fluctuations above T C .
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