The Influence of Magnetic Inhomogeneous State on Thermopower and Magnetothermopower in Sm0.55Sr0.45MnO3 Manganites

Thermopower α and magnetothermopower ∆α/α were studied in the single-crystal Sm0.55Sr0.45MnO3 samples, containing clusters of following three types: ferromagnetic clusters with the Curie temperature TC = 134 K, A-type antiferromagnetic clusters with the Neel temperature TNA ≤ TC and CE-type antiferromagnetic clusters with the TNCE = 240 K. Temperature dependence of α and ∆α/α have extrema in the TNCE-region: large maximum on α(T) and sharp minimum on {∆α/α}(T). Negative magnetothermopower in minimum achieves the giant value 50% in magnetic field H = 13,2 kOe. As will be shown below thermopower is essentially caused by the presence of CE-type antiferromagnetic clusters, in which exists charge order (CO), displacing oxygen ions. Modified crystalline lattice inside clusters causes change of thermopower in them. This thermopower influences on the voltage drop on sample at measurement of thermopower and, consequently, on the effective value α of the whole sample. Enclosure of the magnetic field in the TNCE, which accelerates the destruction of the CE-type antiferromagnetic order, causes sharp decrease of total thermopower. This means that the CE-type antiferromagnetic clusters with CO order are the main contributors to the thermopower of the whole sample.

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