Magnetic Structure, Phase Diagram, and a New Type of Spin-Flop Transition Dominated by Higher Order Interaction in a Localized5fSystemU3Pd

Abstract

The magnetic structure of the localized-5f uranium intermetallic compound U 3 Pd 20 Si 6 has been determined by means of a neutron diffraction experiment. Our data demonstrate that this compound has a collinear coupling of the sublattice ordering of the uranium spins on the 4a and 8c sites. We conclude that higher-order exchange and/or quadrupole interactions are necessary to stabilize this unique collinear structure. We discovered a new type of spin-flop transition against the uniaxial anisotropy induced by this collinear coupling. DOI: 10.1103/PhysRevLett.89.077202 PACS numbers: 75.30.-m, 61.12.Ld Actinide-based intermetallic compound is one of the most attractive systems in the field of strongly correlated electron systems [1]. The main difficulty is how to treat the renormalized quasiparticles, dominating the ground-state properties. Spin and quadrupole degree of freedom with strong Hund coupling should be taken into account for the many-body effect, where the configuration of 5f electrons is very important. However, the configuration in most uranium intermetallic compounds is unknown. Recently, we found a new system, U 3 Pd 20 Si 6 [2,3]. The observation of clear crystalline electric field excitations [4,5] provides direct evidence of the localized nature with the 5f 2 U 4 -ÿ 5 triplet ground state [2,3,5].In addition to the 5f configuration, U 3 Pd 20 Si 6 presents a good opportunity to study a magnetic order which is frustrated due to the cancellation of the Heisenberg interaction between two magnetic sublattices. Our recent neutron scattering study revealed the existence of the successive ordering; uranium spins on the simple cubic 8c lattice order antiferromagnetically below T N 19 K, while the fcc-4a sites show ferromagnetic ordering below T C 2 K [4]. Since the ground-state magnetic structure is unknown, it is unclear whether (and how) the frustration could be released. The origin of the metamagnetic transition also remains an open question [6].In this paper, we report the discovery of a remarkable collinear magnetic structure stabilized by higher-order coupling of an antiferromagnetic 8c lattice to an interpenetrating ferromagnetic 4a lattice. This structure shows a new type of field-induced spin flop caused by the uniaxial anisotropy due to the collinear coupling. The ferromagnetic moment is strongly suppressed by the intersite coupling. The magnetic moment recovers its saturation moment under a magnetic field. The moment size guarantees that this compound is a prototype of the localized 5f magnet with 5f 2 -ÿ 5 ground state.Neutron scattering experiments were carried out on the triple-axis-spectrometer TAS-2 (E i 13:7 meV) at the research reactor JRR-3 in the Japan Atomic Energy Research Institute. A single crystal (0.5 mm thick and 5 mm in diameter) was mounted with the 100 and 011 axes in the horizontal scattering plane. A magnetic field was applied either along the vertical, H ? k 0 1 11 , or horizontal direction, H k k Q. Figure 1 summarizes the H-T phase diagram for the magnetic structures...

The phase stability, magnetic and vibrational properties of A2Ni21B6 (A=Th, U) and Ce3Pd20Si6

“…The cerium and uranium intermetallic compounds have been investigated by a number of workers because of their unusual and interesting physical properties [1][2][3][4][5][6][7][8][9]. These properties arise from the strongly correlated nature of the 4f and 5f electrons and their hybridization with the conduction electrons.…”

Magnetic ordering of hyperfine-coupled nuclear and4f-electron moments in the clathrate compoundPr3Pd20Ge6Iwakami1, Namisashi2, Abe3 et al. 2014Phys. Rev. B3010View full textAdd to dashboardCite

“…1 are the calculated results based on the CEF level scheme and the mean-field approximation. In R 3 Pd 20 X 6 , neutron diffraction experiments demonstrated that the magnetic ordering at the 4a and 8c sites occurs independently at different temperatures [15][16][17]. Furthermore, the CEF level schemes of the 4a and 8c sites in Pr 3 Pd 20 Ge 6 are different.…”

“…The R atoms occupy two crystallographically inequivalent sites: 4a sites with O h symmetry, and 8c sites with T d symmetry. R 3 Pd 20 X 6 have attracted much attention because of their characteristic magnetic ordering with two different propagation vectors on two sublattices, and the quadrupole ordering of f electrons [15][16][17][18][19]. In particular, R 3 Pd 20 Ge 6 have been studied intensively from the viewpoint of rattling motions of a guest rare-earth ion in an oversized cage that are not observed in R 3 Pd 20 Si 6 [20,21].…”