Resonant X-ray diffraction study of multipole ordering in CePdS

Michimura, Shinji; Inami, Toshiya; Matsuoka, Eiichi*; Watahiki, Masanori*; Onodera, Hideya*

Rare-earth palladium bronzes RPdS (R = La-Yb) crystallize in a cubic structure with the space group m-3n. Except for R = Tm, the degeneracy of the orbital degree of freedom is expected to remain in the crystalline electric field (CEF) ground states of R in RPdS. Accordingly, the physical properties will be different from the properties of simple magnetic ordering compounds, since mulitpole order becomes possible too. CePdS orders ferromagnetically below T = 6.3 K. It was found that the magnetic structure of CePdS is canted with a canting angle of 51 by neutron powder diffraction experiments. Such structure occurs in HoBC too, where is caused by the simultaneous occurrence of antiferroquadrupolar (AFQ) and ferromagnetic (FM) orders. This calls for investigating on the quadrupolar ordering in RPdS. We performed resonant X-ray diffraction at the Ce- absorption edge on CePdS to study the states of quadrupolar ordering in the FM state. We observed two reflections forbidden for crystal structure, 300 and 410 reflections. Both reflections grow below T and be unambiguously related to the order parameter. In the azimuthal angle dependence of 410 reflection for both -' and -' scattering processes, the periodicals are about 180 . The intensity of the -' scattering process is about 20 of the intensity of the -' scattering process. This result suggests that an type - AFQ ordering coexists with FM ordering.