ИСТИНА

Currently, practical use of thermoelectricity is mostly limited to thermocouples for temperature measurement. It‘s not applicable in other devices such as thermoelectric generator, refrigerator and heaters due to the low efficiency. It will be shown that the usage for this purposes the heterogeneous magnetic semiconductors can significantly increase the efficiency of devices based on them. Consider a semiconductor inside which is located a one nanocluster with charge carrier concentration and the crystal structure different than in the matrix. Electric current, flowing in the sample during the measurement of thermopower α, causes the Peltier effect at a boundaries of the cluster, i.e. a temperature difference ΔТ, which, in turn, produces thermopower α1 on it. This cluster contribute (α1-α2)ΔТ in thermopower of the whole sample. Here α2 is thermopower of a sample in the absence of nanoclusters. That contribution from nanoclusters affects to the effective value α of the entire sample. Obviously when the sample has a large number of nanoclusters, α value may be considerable. The researching of neutron and electron diffraction and magnetic properties of Sm0.55Sr0.45MnO3 have shown that there is a magnetic inhomogeneous state in it consisting of ferromagnetic (F) clusters with Curie point TC = 134 K, A-type antiferromagnetic (AF) clusters with Neel temperature TNA~TC and CE-type AF clusters with TNCE = 240 K. We have investigated the thermopower a and longitudinal magnetothermopower delta a/a = (αH-αH=0)/αH=0 of the monocrystalline and polycrystalline Sm05.5Sr0.45MnO3 in magnetic field up to 13.2 kOe. The broad maximum on temperature dependence of absolute value α(T) includes TC, but near TC is also the sharp giant minimum on the {delta a/a}(T) curves. Sharp decrease of α in TC under the action of magnetic field is connected with destruction of the F nanoclusters in which the crystalline lattice is pressed by strong s-d exchange. Negative magnetothermopower in its minimum achieves the giant value of 90% in magnetic field H = 14,2 kOe. The changed crystalline lattice in these clusters excites the change of thermopower in them. This cluster‘s thermopower influences on the voltage drop of whole sample during the measurement of thermopower and, consequently, on the effective value α of the whole sample. This means that F clusters make the basic contribution in the total thermopower. Recently we have shown that in Sm0.55Sr0.45MnO3 single crystal annealed in oxygen, in which broken connections Mn-V-Mn (V is vacancy) are closed, CE-type AF phase becomes dominant in the sample. In this case the giant minimum on {delta a/a}(T) curves is sharp and located near the TNCE. Sharp decrease of α in TNCE under the action of magnetic field is connected with destruction of CE-type AF phase and, consequently, destruction of charge ordering, displacing the oxygen ions [1]. [1] L.I. Koroleva, A.S. Morozov, E.S. Jakina. Physics of Solid State, 56 (2014) 1069-1072.