Skip to main content
European Commission logo print header
Contenu archivé le 2022-12-23

Charge/orbital/spin ordering on the verge of Co3+ spin-state transition in the giant magnetoresistive cobaltites

Objectif

The proposed research lies in the general fields of the cobalt and rare earth ions magnetism, spin-lattice dynamics, X-ray resonant/non-resonant diffraction and neutron scattering in perovskite-like cobaltites having a potential for device applications.
The project is aimed at experimental and theoretical studies of the influence of the rare-earth ion radius, oxygen content and temperature on the spin - state of cobalt ions and on the charge/ spin/orbital ordering in the rare-earth cobaltites.
Particular attention will be given to investigation of the magnetic order parameters, rare earth and 3d metal exchange interactions and spin excitations in single crystals of the compounds, which reveal the so called 'giant' magnetoresistance (MR) mostly near the AFM/FM phase boundary.
Another key aspect of this project is a comprehensive study of the 'temperature-pressure-magnetic field-oxygen content' phase diagram in the layered cobaltites at compositions close to the appearance (disappearence) of the ferromagnetic state.
High quality single crystals are essential to achieve the project goals. The original flux growth technology of RCoO3-d (R being rare earth ion in the range La-Yb) and RBaCo2O5+d (R= Nd, Sm, Gd, Ho) has been developed to provide large and high quality single crystals for the research. To introduce charges into oxygen sites of the materials a special electrochemical technique has been developed.

Comparative studies for both families of the cobaltites are suggested by means of the conventional and synchrotron X-ray diffraction, 59Co-NMR, and Raman spectra as well as by investigation of magnetic/transport properties as a function of oxygen content. For this purpose a special electrochemical technique to introduce or remove oxygen from the crystal lattice of the oxides has been developed. The neutron scattering experiments will be also performed. The work will employ both polarized and un-polarised scattering techniques to study the nature of the order parameter, the excitation spectra, and the values of interaction constants.
Both the theoretical symmetry analysis (based on neutron diffraction and Raman results) for the magnetic and crystal structure, and the calculation (by the tight-binding approach) of exchange/ super exchange magnetic interactions of rare earth and Co local magnetic moments either via the neighbouring oxygen or through a vacant site of the [R-?] layer will be carried out.
The applicants also propose to monitor the development of orbital ordering as well the Co3+ spin-state transitions in the cobaltites. For the objective newly proved the X-ray resonant/non-resonant diffraction and photoemission, elastic/inelastic neutron scattering, Raman, and NMR/NQR studies will be undertaken using PSI and SLS, Villigen, ILL and ESRF, Grenoble, CLRC Daresbury Lab and SPNPI, St.-Petersburg synchrotron and neutron facilities, Aachen and Kharkov RLS spectrometers, and resonant equipment at the University of Prague and DPTI, Donetsk.
The band structure calculations based on the using of the local density approximation to the density functional theory for different types of electronic structure of cobalt and for various peculiarities of magnetic ordering both in Co and R sublattices will be performed.
A clear physical picture of the origin of RBaCo2O5+d metallicity as well as of pecularities of orbital/charge/spin order and Co3+ spin-state transitions that develop with changes in temperature and oxygen content will be presented for the double perovskites basing on comparison of experimental and theoretical findings.
The achievement of the stated objectives will fill up a gap in the current understanding of the interplay of structural dimensionality, spin-state transformations, rare earth and cobalt exchange interactions, and the giant MR property in the pure and doped cobaltites.
The combined skills and expertise available within the four INTAS and five NIS groups during of two years cooperation will enable significant progress in this field.

Appel à propositions

Data not available

Régime de financement

Data not available

Coordinateur

Paul Scherrer Institut Villigen
Contribution de l’UE
Aucune donnée
Adresse

5232 Villigen PSI
Suisse

Voir sur la carte

Coût total
Aucune donnée

Participants (8)