A model is developed for the band structure of the Feo.bRho.5 mtiferromagnetic ordered alloy, and the local effects are studied of a substitutional impurity on the electronic and magnetic properties of the host. It is found that anFe impurity substituted for Rh creates a perturbation extending a t least to the nearest neighbours of the impurity, and a total ferromagnetic moment close to 3.5,~~. A Rh impurity substituted for Fe has a localized and less important effect. The influence of the magnetic state of the host and the case of other impurities substituted for Rh are also investigated.On construit nn modkle de bandes pour l'alliage ordonne antiferromagnetique Feo,sRho,S, et on Btudie les effets locaux d'une impuret6 substitutionnelle sur les propriBt6s Blectroniques et magri6tiques de la matrice. On trouve qu'une impuret6 defer substitube au rhodium cr6e une perturbation qui s'ktend au moins jusqu'aux premiers voisins de I'impuretB et un moment total voisin de 3,5pu. Une impuretk de Rh substitube au fer produit un effet localis6 et moins important. On examine Bgalement I'influence de 1'Btat magnhtique de la matrice et le cas dautres types d'impureths substitukes au rhodium.

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2014 Nous étudions la structure électronique au niveau des premiers voisins d'un atome de fer substitué à un atome de rhodium dans un composé stoechiométrique de FeRh. La structure de bandes antiferromagnétique du composé binaire FeRh est décrite par une méthode de liaisons fortes. L'effet de la substitution est décrit par un potentiel perturbateur présentant des éléments de matrice intrasite et intersite limités à l'impureté et à ses premiers voisins. Notre modèle montre une tendance à un renversement de la direction du moment sur la moitié des premiers voisins de l'impureté, ceux qui étaient au départ antiparallèles à la direction du champ appliqué. Cet effet peut conduire à l'apparition de moments géants, ainsi qu'il a été suggéré expérimentalement.Abstract. 2014 Within a tight-binding scheme, we study the local electronic structure on the nearest-neighbours of a rhodium site which has been substituted by an iron impurity in the stoichiometric FeRh compound in its antiferromagnetic phase. The replacement of the rhodium atom is described by an extended perturbation potential which includes changes in the intrasite and intersite matrix elements up to the first nearest-neighbour shell of the point defect site. Our model shows that a spin-flip on the nearest-neighbour site of the substituted atom, antiparallel to the direction of the applied field is energetically favourable. This could lead to the nesting of a giant moment as has been suggested experimentally. J. Physique 42 (1981) 573-577 AVRIL 1981, Classification Physics Abstracts 75.50E -75.10L

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The space–time step–step correlations of a polymer chain, described by a self‐avoiding random walk on a cubic lattice, are studied by simulating its behavior on a computer. Chains of N = 16 and N = 32 beads are studied. The short‐time behavior of the correlations is characterized by peaks, which become depressed and broadened with increasing interstep distance. The long‐time behavior is characterized by extremely slow decay, which goes to zero in about the same time for all interstep distances. The short‐time behavior is a consequence of the rotation of parts of the chain smaller than or equal to the static coherence length ζ. These short‐time processes also seem to be responsible for the relaxation of the square of the end‐to‐end distance, since in both cases the relaxation is of the order of 6N2. The long‐time behavior of the correlations is a consequence of the rotations of parts of the chain greater than the coherence length. The correlations vanish when the entire chain has had time to rotate in space. Our results suggest that this corresponds to the relaxation of the end‐to‐end vector.