Among nanostructured metal-oxides an increased attention is given to rare earth manganites and cobaltites, in which a colossal magnetoresistive effect (MR) has been revealed. Practical interest is caused by manganite-lanthanum perovskites, containing surplus superstoichiometric manganese.

By the X-ray, resistive, magnetic and NMR of ⁵⁵ Mn methods the phase composition, defectiveness of perovskite structure, metal-semiconductor (T_ms) and ferro-paramagnetic (T_c) phase transitions, magnetoresistance effect (T_p), local magnetic and charge states of manganese in nonstoichiometric manganite-lanthanum-strontium perovskites La_0,6Sr_0,2Mn_1,2-xCo_xO₃ have been investigated.

Phase composition of ceramic samples is specified. It is shown that perovskite structure (R-3c) contains Mn³⁺_B, Mn⁴⁺_B, Mn²⁺_A ions, anionic and cationic vacancies (in A- and B-sublattice) and which are in high-frequency electron-hole exchange slim nanostructure clusters with Mn²⁺ in deformed A-sublattice. Such character of defectiveness of structure is confirmed by computer decomposition of NMR ⁵⁵ Mn spectra and their analysis taking into account the irregular surroundings of manganese ions by both other ions (La³⁺, Sr²⁺, Mn²⁺, Co³⁺) and defects with cluster type nanostructure.

Со³⁺ ions, substituting Mn³⁺ ions, lower magnetization (М) and temperatures T_c, T_p and less distinctly T_ms. Clusterization, related to the surplus manganese was confirmed by hysteresis of temperature dependences for M belov 45 K.

The tendency of MR enhancement by T_p, which is connect with defective crystal structure, and of MR lowering by 77 K, caused by tunneling along intercrystallite zones, that is (i.e.) mesoscopic inhomogeneity of ceramic samples has been determined.

On the basis of analysis of the results a conclusion is made on regularities of Co effect on nano- and mesostructures inhomogeneity, on the phase transitions, transport and magnetic properties of doped manganite-lanthanum perovskites.

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