Neutron-diffraction study of the magnetic and orbital ordering in (SmNiO3)-Sm-154 and (EuNiO3)-Eu-153

Article

关键词: METAL-INSULATOR-TRANSITION;    PEROVSKITES RNIO3 R=PR;    MAGNETORESISTANCE;    ND;    OXIDES;    FILMS;    FIELD;   

DOI  :  10.1103/PhysRevB.57.456

来源: SCIE

【 摘 要 】

Neutron-powder-diffraction experiments on (SmNiO3)-Sm-154 and (EuNiO3)-Eu-153 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 Neel temperature (T(M-I)approximate to 400 K, T-N approximate to 230 K for Sm and T(M-I)approximate to 480 K, T-N approximate to 220 K 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 Phnm 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.

【 授权许可】

Free