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Accueil du site > Vie du Laboratoire > Archives > Archives 2015 "A la Une"

Archives 2015 "A la Une"

Ferromagnetism and Phase Separation of Strongly Correlated Electrons

In this work we focus on the extended nondegenerate Hubbard model which describes the simplest correlated metals and investigate the influence of intersite Coulomb and exchange interactions on the charge and magnetic instabilities. We present numerical analysis for a representative example of a three-dimensional cubic lattice. To that aim we adopt and extend the spin-rotation-invariant Kotliar and Ruckenstein slave boson representation.

Instability lines of the unpolarized state towards ferromagnetic order as given by the divergence of the magnetic susceptibility for the Hubbard model extended by a ferromagnetic exchange J<0 on the cubic lattice. Different lines from top to bottom for : J/U=0, -0.01, -0.05, -0.1, -0.15, -0.2.

Landau parameters Fs0 for the Hubbard model on the cubic lattice extended by attractive density-density interactions V/U = -0.2. Ferromagnetic and charge instabilities are found in large regions of the phase diagram.

By : G. Lhoutellier, R. Frésard et A. M. Oles,
Phys. Rev. B 91, 224410 (2015)

Nouveaux Matériaux : Fondements, Fonctionnalités (NMF2)

La1-xLnxH(O3PCH3)2 : an organic–inorganic hybrid with lanthanide chains and tunable luminescence properties

The photoluminescence of Eu3+, Tb3+ and Eu3+/Tb3+ co-doped La1-xLnxH(O3PCH3)2 (Ln=Eu,Tb) hybrids have been investigated. The crystal structure of LaH(O3PCH3)2 consists of chains of edge-sharing LaO8 polyhedra linked through PO3C tetrahedra. The Eu and Tb hybrids show no concentration quenching versus doping rate suggesting energy migration through a percolation model. The Eu hybrids exhibit a red emission while the Tb ones exhibit, with the Tb rate increasing, a blue to green emission under a 378 nm excitation wavelength and a cyan to green emission under a 262 nm excitation wavelength.

B. Mutelet, S. Boudin, O. Pérez, J. M. Rueff, C. Labbé and P.A. Jaffrès
Dalton Trans. 44 (2015) 1186-1192. DOI : 10.1039/C4DT02643H

Corresponding author : Sophie Boudin

Hétérostructures et Oxydes à Propriétés Electroniques (HOPE)

Structural transition at 360 K in the CaFe5O7 ferrite : toward a new charge ordering distribution

Une analyse structurale de CaFe5O7 par microscopie électronique (TEM, STEM-HAADF) et diffraction par les rayons X a révélé une transition réversible (monoclinique-orthorhombique) à 360K. Ce phénomène a été étudié conjointement par spectroscopie Mössbauer et par des mesures magnétiques et électriques : une discontinuité est nettement observée associée à une nouvelle configuration électronique.

Delacotte C, Hüe F, Bréard Y, Hébert S, Pérez O, Caignaert V, Greneche JM, Pelloquin D.
Inorg Chem. 53, 10171 (2014)- DOI : 10.1021/ic5011456

Hétérostructures et Oxydes à Propriétés Electroniques (HOPE)

Random dilution effects in the frustrated spin chain ß-CaCr2-xScxO4

Random dilution effects in the magnetic zigzag ladder (J1 -J2 chain) ß-CaCr2-xScxO4 have been investigated combining magnetic susceptibility, specific heat measurements, and neutron scattering. The pseudogapped magnetic excitations observed above TN in x=0 (21 K) persist up to x=0.3 with an increasing characteristic frequency E0, but vanish for x=0.5 for which a quasielastic signal extending up to 8meV becomes the characteristic feature of the magnetic spectrum. Magnetic ordering is seen up to x=0.3 with decreased ordering temperature TN and correlation length. The results are interpreted in terms of the progressive confinement of one-dimensional excitations within shorter chains as x increases, and emphasize the crucial role of J2 in propagating magnetic excitations.

M. Songvilay, S. Petit, V. Hardy, J. P. Castellan, G. André, C. Martin, and F. Damay.
Phys. Rev. B 91, 054408 (2015).

Physique et Structures d’Oxydes Magnétiques (PSOM)