ИСТИНА

In the example of Sm0.55Sr0.45MnO3 manganite, having magnetic clusters of different types, it is shown that its thermopower is largely determined by the presence of clusters. This opens a new way to increase the thermopower by increasing the concentration of clusters. Thermopower α and magnetothermopower ∆α/α are studied in the single-crystal Sm0.55Sr0.45MnO3 samples, containing clusters of the 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 curves of α and ∆α/α have the following 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 of 50% in magnetic field H = 13,2 kOe. It is shown that thermopower is essentially caused by the presence of CE-type antiferromagnetic clusters, in which there is a charge order (CO), dislocating oxygen ions. The changed crystalline lattice in these clusters excites the exchange of thermopower in them. This thermopower influences on the voltage drop on a sample during measurement of thermopower and, consequently, on the effective value of α of the whole sample. Enclosure of the magnetic field in the TNCE, accelerated the destruction of the CE-type antiferromagnetic order, causes the sharp decrease of thermopower of the whole sample. By this is meant that the CE-type antiferromagnetic clusters with CO order make the basic contribution in the thermopower of the whole sample.