Sm金属間化合物における新奇な量子秩序相

首都大学東京, 2016-03-25, 博士（理学）, 甲第566号首都大学東

Atomic displacements and lattice distortion in the magnetic-field-induced charge-ordered state of SmRu4P12

Structural properties of SmRu4P12 in the anomalous magnetic ordered phase between T∗∼14 K and TN=16.5 K in magnetic fields has been studied by x-ray diffraction. Atomic displacements of Ru and P, reflecting the field-induced charge order of the p electrons, have been deduced by analyzing the intensities of the forbidden Bragg peaks, assuming a cubic space group Pm3¯. Also, by utilizing a high-resolution x-ray diffraction experiment, we observed a splitting of fundamental Bragg peaks, clarifying that the unit cell in the magnetic ordered phase is rhombohedral elongated along the [111] axis. The response of the rhombohedral domains to the magnetic field, which reflects the direction of the magnetic moment, is studied in detail

Magnetic-field-induced charge order in the filled skutterudite SmRu4P12 : Evidence from resonant and nonresonant x-ray diffraction

The antiferromagnetic ordered phase in SmRu4P12 below the metal-insulator transition at T MI = 16.5 K with an unresolved transition at T∗ ～ 14 K has been studied by resonant and nonresonant x-ray diffraction in magnetic fields. In the intermediate phase, a nonresonant Thomson scattering with q = (1,0,0) is induced by applying a magnetic field, which is presumably caused by atomic displacements reflecting the charge order in the p band, as predicted theoretically [R. Shiina, J. Phys. Soc. Jpn. 82, 083713 (2013)]. Simultaneously, the antiferromagnetic moment of Sm is enhanced along the field direction, which is considered to reflect the staggered ordering of the Γ 7 −Γ 8 crystal-field states (scalar or hexadecapole order). The present results show that the orbital-dependent p-f hybridization in association with the nesting instability in the p band gives rise to the unconventional charge order similarly with PrRu4P12 and PrFe4P12.This work was supported by Grants-in-Aid for Scientific Research (No. 21204456, No. 21102515, and No. 2430087) from JSPS and MEXT, and by a Basic Science Research Grant from the Sumitomo Foundation

Isotropic parallel antiferromagnetism in the magnetic field induced charge-ordered state of SmRu4P12 caused by p−f hybridization

Nature of the field-induced charge-ordered phase (phase II) of SmRu4P12 has been investigated by resonant x-ray diffraction (RXD) and polarized neutron diffraction (PND), focusing on the relationship between the atomic displacements and the antiferromagnetic (AFM) moments of Sm. From the analysis of the interference between the nonresonant Thomson scattering and the resonant magnetic scattering, combined with the spectral function obtained from x-ray magnetic circular dichroism, it is shown that the AFM moment of Sm prefers to be parallel to the field (mAF // H), giving rise to large and small moment sites around which the P12 and Ru cage contract and expand, respectively. This is associated with the formation of the staggeredordering of the Γ7-like and Γ8-like crystal-field states, providing a strong piece of evidence for the charge order. PND was also performed to obtain complementary and unambiguous conclusion. In addition, isotropic and continuous nature of phase II is demonstrated by the field-direction invariance of the interference spectrum in RXD. Crucial role of the p- f hybridization is shown by resonant soft x-ray diffraction at the P K edge (1s ↔ 3p), where we detected a resonance due to the spin polarized 3p orbitals reflecting the AFM order of Sm