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Inhomogeneous states and the effects of isotope substitution in magnetic oxides

Project information

Grant agreement ID: INTAS-2001-02008

  • Start date

    1 June 2002

  • End date

    31 May 2004

Funded under:

IC-INTAS

Coordinated by:

Institut des sciences de la Matière et du rayonnement (ISMRA)

France

Objective

The project is aimed at revealing the main characteristic features of inhomogeneous states of different types (superstructures, stripes, random percolation networks) in doped magnetic oxides, notably in CMR manganites, using in particular the isotope effects in them. Isotope substitution allows one to "gently" influence the properties of corresponding compounds without changing the chemical composition, and at the same time it is capable to profoundly modify the state of these systems. The complex study of isotope effects for different type of systems (polycrystals, films, artificial structures) using various experimental techniques (structural studies by X-ray diffraction, neutron scattering, and electron microscopy; transport and magnetic measurements; study of ESR and NMR on La, Mn, 17O; optical investigations) would allow us to obtain a comprehensive picture of the behaviour of these systems, in particular, the role played by electron-lattice interactions and polaron effects, which apparently are crucial in determining the structure and properties in inhomogeneous states.

According to these goals the research will be focused on the following tasks:
(i) analysis of different types of phase separation and charge/orbital ordering in complex magnetic oxides;
(ii) the study of the isotope effect in the systems with phase separation;
(iii) manufacturing and investigation of artificial inhomogeneous structures.

The performing of these tasks will involve:
- synthesis of mixed rare-earth manganites and related perovskite-like oxides and preparation of the samples in the form of single crystals, epitaxial films, pellets, powders, and artificial superstructures;
- oxygen isotope substitution of the samples (using both 18O and 17O);
- characterization of crystal and magnetic structure of the samples and their homogeneity by X-ray diffraction, electron microscopy, neutron scattering, muon spectroscopy, and optical methods;
- NMR (17O, 55Mn, 139La) and ESR studies of inhomogeneous states;
- measurements of dc conductivity, current-voltage characteristics, ac magnetic susceptibility, and dc magnetization as function of temperature and magnetic field with the emphasis on the isotope effect and especially on the metal-insulator transition induced by the isotope substitution;
- interpretation of experimental data in the framework of microscopic models accounting for the electron-lattice coupling (manifesting itself in large isotope effect), strong electron correlations resulting in the interplay of charge, orbital, and magnetic ordering, as well as in phase separation.

As a result, it is expected to produce a set of magnetic oxides exhibiting different kinds of inhomogeneous states, to find out the local structure of such states, to reveal the effect of isotope substitution on the phase diagrams and transport properties. These results should provide a clue to microscopic nature of intrinsic inhomogeneities and the giant isotope effect in doped magnetic oxides with competing order parameters in the situation with strong electron-electron correlations accompanied by pronounced electron-lattice coupling.

Coordinator

Institut des sciences de la Matière et du rayonnement (ISMRA)

Address

6, Boulevard Du Marechal Juin
14050 Caen Cedex

France

Participants (7)

All-Russia Electrical Engineering Institute

Russia

Joint Institute for Nuclear Research

Russia

Kapitza Institute for Physical Problems

Russia

M.V. Lomonosov Moscow State University

Russia

Russian Research Center "Kurchatov Institute"

Russia

University of Cambridge

United Kingdom

University of Groningen

Netherlands

Project information

Grant agreement ID: INTAS-2001-02008

  • Start date

    1 June 2002

  • End date

    31 May 2004

Funded under:

IC-INTAS

Coordinated by:

Institut des sciences de la Matière et du rayonnement (ISMRA)

France