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Article Dans Une Revue Physical Review B: Condensed Matter and Materials Physics (1998-2015) Année : 1998

Neutron-diffraction study of the magnetic and orbital ordering in 154SmNiO3 and 153EuNiO3

Résumé

Neutron-powder-diffraction experiments on 154SmNiO3 and 153EuNiO3 at different temperatures have been performed. At variance with the case of Pr and Nd nickelates, the metal-insulator transition temperature in these compounds are different from the Néel temperature (TM−I≈400K, TN≈230K for Sm and TM−I≈480K, TN≈220K for Eu) so that the magnetic ordering develops upon cooling in an insulating matrix. With decreasing temperature the crystal structure undergoes a 0.15% lattice expansion at TM−I. The crystal symmetry Pbnm does not change within the experimental error, but the Ni-O average distance increases and the superexchange angle Ni-O-Ni decreases slightly in the insulating regime. The magnetic structure of both compounds has the same propagation vector k=(1/2,0,1/2) as observed in Pr and Nd nickelates. This feature leads us to speculate that the orbital ordering responsible for the magnetic structure is a characteristic of the insulating state of the RNiO3 series (at least for light rare earths R). A search for small nuclear superstructure peaks characterizing the orbital ordering has been carried out without success. The consequences of our experimental results are discussed in the context of current ideas about superexchange in oxides.
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Dates et versions

hal-02196537 , version 1 (29-07-2019)

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J. Rodriguez-Carvajal, S. Rosenkranz, M. Medarde, P. Lacorre, M. T Fernandez-Diaz, et al.. Neutron-diffraction study of the magnetic and orbital ordering in 154SmNiO3 and 153EuNiO3. Physical Review B: Condensed Matter and Materials Physics (1998-2015), 1998, 57 (1), pp.456-464. ⟨10.1103/PhysRevB.57.456⟩. ⟨hal-02196537⟩
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