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A large intrinsic magnetoresistance has been found near the ferromagnetic transition of metallic manganese oxides with perovskite-type crystal structure. The magnetic and transport properties were measured on bulk and thin-film La1−xAxMnO3+δ with A=Ca,Sr,Ba. Assuming the double-exchange model proposed by Zener [Phys. Rev. 81, 440 (1951); 82, 403 (1951)], the strong dependence of the transport properties on the magnetic field and also on the chemical composition is attributed to the mixed Mn3+/Mn4+ valence.
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Helmolt et al. (1994) studied this question.
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