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Magnetic and magnetotransport properties in (Lax Sm1–x )2/3Sr1/3MnO3 (x = 1/3, 1/2 and 2/3) manganites

The magnetic and transport properties of (Lax Sm1–x )2/3Sr1/3MnO3 (x = 1/3, 1/2 and 2/3) manganites, prepared by the citrate‐gel route, have been investigated. These compounds are found to crystallize in the orthorhombic structure. The hopping between Mn3+ and Mn4+ sites is controlled by the Mn–O–Mn bond angle. The magnetoresistance in 8.5 kOe fields varies from 15 to 25 percent over the temperature range 300 K to 80 K. The conduction mechanism can be understood by using the correlated small polaron model. The metal–insulator as well as magnetic transition temperatures are close to each other, which indicates the dominance of long‐range ferromagnetic ordering in the present system. At low temperatures, a weak ferromagnetic to antiferromagnetic transition is indicated, which could be due to competing superexchange and double exchange interactions. The charge localization at lower temperatures could be the possible explanation for increasing magnetoresistance. The maximum magnetic moment at 5 K, for all the samples is ∼3.6μ B/Mn, which is close to the 3.7μ B/Mn, as obtained by considering the Mn spins only. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)