Ce multipoles in phase IV of Ce0.7La0.3B6 inferred from resonant x-ray Bragg diffraction

Low temperature properties of Ce0.7La0.3B6 in zero external magnetic field in a small temperature range, below 1.4 K, point to the existence of a phase IV characterized by a nonconventional electron ground state with no ordering of 4f magnetic dipole Ce moments. We report a successful analysis of extensive observations on phase IV made by resonant x-ray Bragg diffraction at the Ce L-2 absorption edge. In the analysis, we explore contributions to diffraction by the four domains arranged with triad axes placed along [111], [11 (1) over bar], [1 (1) over bar1], and [(1) over bar 11] and from all possible Ce multipoles up to hexadecapoles. Ce quadrupoles and octupoles adequately represent intensity observed in the azimuthal-angle scans for both rotated and unrotated polarization channels at the Bragg reflection (3/2 3/2 3/2) measured by Mannix [Phys. Rev. Lett. 95, 117206 (2005)]. In this scenario, the magnetic properties of the alloy are due to an antiferromotif of octupoles. While the antiferroquadrupole contribution calculated for (3/2 3/2 3/2 a small influence in the azimuthal-angle dependence we predict that for the reflection (1/2 1/2 1/2) this contribution would radically influence the azimuthal dependence of the intensity. We demonstrate that available data are adequately described also by one microdomain with antiferro-ordering of Ce octupoles and hexadecapoles. In this case, octupole ordering signifies the departure from a cubic chemical structure.