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Nanostructure clusterization, phase transitions and magnetoresistive properties of nonstoichiometrical perovskites La0,6Sr0,2Mn1,2-xCoxO3 (x=0-0,3)

Pashchenko Valentin 1Prokopenko Vasilij 1Pashchenko Aleksey 1,2Revenko Yuriy 1Shemyakov Aleksandr 1Kisel Nikolay 1Hanna Silcheva 2Igor Zhikharev 1,2Dyakonov Vladimir 2,3Szymczak Himrik 3

1. Donetsk Institute for Physics and Engineering, NASU, Donetsk 83114, Ukraine
2. Luhansk Taras Shevchenko National Pedagogical University, Luhansk 91011, Ukraine
3. Polish Academy of Sciences, Institute of Physics, Warszawa 02-668, Poland


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 (Tms) and ferro-paramagnetic (Tc) phase transitions, magnetoresistance effect (Tp), local magnetic and charge states of manganese in nonstoichiometric manganite-lanthanum-strontium perovskites La0,6Sr0,2Mn1,2-xCoxO3 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 Tc, Tp and less distinctly Tms. Clusterization, related to the surplus manganese was confirmed by hysteresis of temperature dependences for M belov 45 K.

The tendency of MR enhancement by Tp, 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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Presentation: Poster at E-MRS Fall Meeting 2007, Symposium A, by Hanna Silcheva
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-11 16:44
Revised:   2009-06-07 00:44