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Magnetismus Poster: Do., 13:00–15:30 D-P223
XAFS and neutron diffraction study of the the La1−xSr(Ba)xCoO3 and
La1−xSrxCo1−x/2Nbx/2O3
Vadim Efimov 1 , Sergey Tiutiunnikov 1 , Dmitriy Kochubey 2 , Vladimir
Kriventsov 2 , Aleksandr Shmakov 2 , Igor Troyanchuk 3 , Alexey Kuzmin 4 ,
Vadim Sikolenko 5 , Serguei Molodtsov 6 , Denis Vyalikh 6
1 Joint Institute for Nuclear Research (JINR), 141980 Dubna, Moscow region, Russia
– 2 Boreskov Institute of Catalysis, Lavrentiev prosp. 5, Novosibirsk, 630090, Russia –
3 Institute of Solid State and Semiconductor Physics, 220072 Minsk, Belarus – 4 Institute
of Solid State Physics University of Latvia, 8 Kengaraga, Riga LV-1063, Latvia –
5 Hahn-Meitner-Institut Glienicker str. 100 Berlin D-14109 Germany – 6 Institut f.
Festkoerperphysik Fachrichtung Physik TU Dresden 01062 Dresden, Germany
The discovery of the colossal magnetoresistance (CMR) in the manganites with perovskite
structure [1] has stimulated the research of the compounds exhibiting large
magnetoresistance. The magnetic and transport properties of La1−xSrxCoO3 cobaltites
with perovskite structure and manganites such as La1−xSrxMnO3 have common features
[2]. In both systems the substitution of La with divalent ion Sr creates paramagnetic
(x0.3) transition as the dopant concentration is
increased. The Sr 2+ and especially Ba 2+ ionic radiuses is significantly greater than that
of the La 3+ ion, so it is possible to expect stabilization of the intermediate spin state of
cobalt ions by substituting Sr 2+ and especially Ba 2+ ions for La 3+ ones. However, at
such heterovalent substitution Co 4+ ions appear, leading to the ferromagnetic metallic
ground state [3]. To prevent the Co 4+ ion appearance, it is possible to introduce
simultaneously Nb [4] ions, which at the presence of Co 3+ ions will be in oxidizing
state 5+. By simultaneously introducing Sr 2+ and Nb 5+ the cobalt ions keep their
valence state and the electroconductivity of La1−xSrxCo1−x/2Nbx/2O3 solid solutions
decreases with dopant concentration enhancement.Thus, the different nature of ferromagnetic
interactions formation in the given systems is obvious [4]. In this work we
present EXAFS and XANES measurements at the Co K-edge in La1−xSr(Ba)xCoO3
and La1−xSrxCo1−x/2Nbx/2O3 (x = 0; 0.2; 0.3; 0.5) solid solutions. The sensitivity
XANES and EXAFS to chemical composition, local lattice distortion, “chemical pressure”
effect and to an overlapping mixture of low, intermediate and high spin states
of Co 3+ and Co 4+ ions in these cobaltites was also considered. Crystal and magnetic
structure of these cobaltites were precisely determined by high-resolution X-ray
and Neutron diffraction methods. Correlations of the long-range structure parameters
with local atomic and electronic structure ones and also with SQUID magnetization
measurements was analyzed. The details of local atomic and electronic structure in
cobaltites doped by Sr, Ba and Nb are presented and discussed.
[1] P.M. Raccah and J.B. Goodenough, Phys. Rev. 155, 932 (1967).
[2] G. Briceno et.al. Science 270, 273 (1995).
[3] J. Wu, C. Leighton, Phys. Rev. B 67(17), 174408 (2003).
[4] I.O. Troynchuk,et.al.,Phys. Stat. Sol.B 242, No. 6, pp. 49-51 (2005).