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Studies of magnetoresistance of manganite-lanthanum perovskites

Igor Zhikharev 1,2Valentin P. Pashchenko 1Aleksey V. Pashchenko 1Aleksandr A. Shemiakov 1Vasilij K. Prokopenko 1Hanna Silcheva 2

1. National Academy of Sciences of Ukraine, Donetsk Technical-Physical Institute, R. Luxemburg 72, Donetsk 83114, Ukraine
2. Luthansk State Pedagogical University, Luthansk, Ukraine


High-temperature X-ray analysis and magnetoresistance method allow us to reveal the anomalous behaviour of crystalline-lattice parameter of La0,6A0,2Mn1,2O3delta (A2+: Ca2+, Sr2+, Pb2+) near the temperatures of transitions - Tc, Tm (colossal magnetoresistance), and Tp. The sample consists of a single phase. The La0,6A0,2Mn1,2O3delta (A2+: Sr2+, Pb2+) - structure is rhombohedral (R3c) and includes the plane clusters of gamma-Mn2O3 or Mn3O4 types [1]. The clusters are dissolved in the matrix structure, when the temperature is increased and the matrix structure is transformed into the cubic one at the temperatures within the range 1070-1100 K (Pm3m). Structure La0,6Ca0,2Mn1,2O3delta is cubic (Pm3m), but also consist the plane clusters of gamma-Mn2O3 or Mn3O4 types [2].
The linear relationship is determined between the width of NMR spectrum from octahedral manganese ions taking place in a high-frequency electronic exchange and the tolerance factor calculated for defect structure accounting the infringement of a co-ordination number, giving rise to distortions of polyhedrons owing to anionic vacancies.
The broad asymmetric NMR spectra suggest that there is a high-frequency electron exchange between Mn3+ and Mn4+ and that the environment of Mn3+, Mn4+ and La3+ is nonequivalent because of the vacancies and clusters and different valence of the ions.
Probably, the origin of the structural anomaly is Mn2++Mn4+2Mn3+ transformation or transition of Mn3+ ions from low-spin state into high-spin one.


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Presentation: oral at E-MRS Fall Meeting 2004, Symposium A, by Igor Zhikharev
See On-line Journal of E-MRS Fall Meeting 2004

Submitted: 2004-05-14 12:27
Revised:   2009-06-08 12:55