Resonant x-ray scattering study of magnetic-dipole and electric-quadrupole order in U0.75Np0.25O2

Article

关键词: NEUTRON-DIFFRACTION;    URANIUM-DIOXIDE;    POLARIZATION DEPENDENCE;    EXCHANGE SCATTERING;    U1-XNPXO2 FLUORITES;    NEPTUNIUM DIOXIDE;    PHASE-TRANSITION;    NPO2;    UO2;    ANTIFERROMAGNETISM;   

DOI  :  10.1103/PhysRevB.70.214402

来源: SCIE

【 摘 要 】

We have used element-specific x-ray resonant scattering to investigate the M-4,M-5 edge resonances in a single crystal of U0.75Np0.25O2. Earlier neutron diffraction and Mossbauer studies have shown the presence of long-range antiferromagnetic order below T-N=19 K, with sizeable magnetic moment both on the U and the Np ions. Our resonant x-ray scattering results confirm the presence of an ordered dipole magnetic moment on the Np ions, but also reveal the presence of an antiferro arrangement of the electric-quadrupole moments on both U and Np ions, with the same propagation vector that defines the magnetic structure. From the azimuthal dependence of the intensities we are able to determine the exact configuration of the quadrupolar ordering. The intensities of Bragg peaks associated with magnetic-dipole and electric-quadrupole order have different temperature dependences. On cooling below T-N, the magnetic-dipole order develops faster on the uranium ions, with magnetic order on the Np ions increasing at a lower rate. At the same temperature, quadrupolar order on both the U and Np ions occurs along with an internal Jahn-Teller lattice distortion.

【 授权许可】

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