Modèle pour la structure électronique des composés perovskites du manganèse 01/1975; 36(12). DOI: 10.1051/jphys:0197500360120131700


A theoretical model is proposed which could explain the magnetic and structural phase transitions which have been observed in perovskite compounds MMn 3X (M = metal, X = N or C). By applying the tight binding approximation to d électrons of Mn and p électrons of N, we find a sharp singularity in the electronic density of states at the Fermi level. This singularity could explain the nature of the magnetic phase transition, and the anormal behaviour of the susceptibility in the paramagnetic phase. The structural phase transition would be produced by a Jahn Teller type of effect. Nous proposons un modèle théorique qui semble pouvoir expliquer les transitions de phase magnétiques et cristallines observées dans les composés perovskites du type MMn3X (M = métal, X = N ou C). En appliquant l'approximation des liaisons fortes aux électrons d du manganèse et aux électrons p de l'azote, nous trouvons une forte singularité dans la densité d'états électroniques au niveau de Fermi. L'existence de cette singularité peut expliquer la nature des transitions magnétiques et le comportement anormal de la susceptibilité dans la phase paramagnétique. Le changement de phase cubique → tétragonale est alors attribué à un effet Jahn Teller sur la structure de bande.

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    ABSTRACT: More than thirteen compounds of the series Mn3MX (X = N, C; M = metal) were analyzed by neutron diffraction, magnetic measurements, NMR and Mössbauer effect. Their magnetic and crystallographic properties are related to the electronic concentration essentially depending on the position of M in the periodic table.
    Physica B+C 01/1977; 86(JAN-M). DOI:10.1016/0378-4363(77)90373-4
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    ABSTRACT: In this study of metallic perovskites Mn3MX (M=metal, X=C, N) we emphasize the influence of the (outer) electron concentration on the sequences of crystallographic transitions, on the magnetic ordering temperatures and on the constant (Pauli-type like) part of the magnetic susceptibility. A great variety of observed magnetic structures and transitions (including spin rotations) are described for carbides and nitrides. The Labbé-Jardin tight binding model which invokes a p-dII hybridization between N and Mn orbitals having their energy levels near to the Fermi surface provides the possibility of great variations of the density of states versus temperature and is in qualitative agreement with experiment. It also explains that small substitutions on X have a more drastical effect than those can M.
    Journal of the Physical Society of Japan 03/1978; 44(3):781-791. DOI:10.1143/JPSJ.44.781 · 1.59 Impact Factor
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    ABSTRACT: The octahedral symmorphic space group O1h is the symmetry group of the simple cubic. the caesium chloride, the perovskites and the rhenium trioxide structures. The direct products of irreducible representations of the double space group O1h are reduced for the four points of highest symmetry of the Brillouin zone. Les produits directs de représentations irréductibles du groupe double O1h (groupe de symétrie de la structure cubique simple et de celles du chlorure de césium, des perovskites et du trioxyde de rhénium) sont réduits pour les quatre points de symétrie maximum de la zone de Brillouin.
    05/1978; 39(5). DOI:10.1051/jphys:01978003905052600
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