Ordering and Crossover in a Pseudo-Sextet Localized Electron Model –Possible Scenario for SmRu₄P₁₂Skutterudite–

Abstract

A crystalline electric field (CEF) model of localized 4f 5 electrons is proposed for understanding intriguing ordering phenomena in SmRu 4 P 12 . We take the CEF quartet and doublet (pseudo-sextet) of the Hund's rule ground state with J ¼ 5=2, and include intersite interactions between multipoles by the mean-field theory. The model leads to a multipole order with representation À 5u , and shows the following features: (i) increasing transition temperature T MI with increasing magnetic field; (ii) an anomaly in specific heat and other thermodynamic quantities at lower temperature T ? , (iii) sharpening of the anomaly at T ? as the magnetic field increases. These behaviors reproduce salient features observed experimentally in SmRu 4 P 12 . Possible mechanisms for spontaneous magnetic moment are discussed.

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

“…Magnetic dipole moment of 0.3 µ B observed in the experiment 29,31 is more consistently interpreted as the magnetic dipole of the Γ 7 CF-state (0.24 µ B ), but is difficult to explain by the Γ 5u octupole ordering model, which gives extremely small dipole moment. 32 The fieldinduced atomic displacement clarified in the present work (P m3 model) is more consistent with the Γ 1g order parameter, i.e., the CO or the hexadecapole order of total symmetry, than the Γ 4g hexadecapole. As clearly shown in Fig.…”

“…As studied in Ref. 32, a similar phase diagram can be reproduced by considering a mixed order of Γ 5u octupole and Γ 4g hexadecapole, where the boundary at T * is interpreted as a crossover with a Schottky anomaly. However, the signal of resonant scattering reported in Ref.…”

“…Initially, to interpret this intermediate phase, a possibility of magnetic octupole order was proposed as a primary order parameter. [30][31][32] However, in spite of intensive experimental studies, the microscopic nature of the ordered phases in SmRu 4 P 12 has remained unresolved.…”

High-pressure synthesis of new filled skutterudite compounds SrT 4As12 (T = Fe, Ru, Os)

“…204). 1,2) Filled skutterudite compounds, especially compounds including Ln, have attracted considerable attention owing to their wide variety of strongly correlated electron behaviors, 3,4) such as anomalous metal-insulator transition, 5,6) multipole ordering, [7][8][9][10][11] and unconventional superconductivity. 12,13) The various attractive features in these systems are believed to be mainly due to the large hybridization between the f electrons of Ln and the p electrons of X.…”

p–f Mixing, Competing Interactions, and Unconventional Magnetism in SmRu4P12

“…In order to explain some aspects of the anomalies, higher-rank magnetic multipoles have been proposed as the primary order parameter. [12,18,22,23] It should be stressed, however, that a recent neutron scattering experiment clarified the existence of a sizable Sm magnetic moment 0.3 µ B at zero magnetic field and that its magnetic form factor was explained by the dipole approximation, in which the contribution of high-rank multipoles is neglected. [20] Therefore, the predominant component of the order parameter can be dipole although a mixture with the octupoles cannot be excluded.…”