67 research outputs found
Low-Temperature X-ray Crystal Structure Analysis of the Cage-Structured Compounds MBe13 (M = La, Sm, and U)
The beryllides MBe13 (M = rare earths and actinides) crystallize in a
NaZn13-type cubic structure, which can be categorized as a cage-structured
compound. In this study, powder X-ray diffraction measurements have been
performed on LaBe13, SmBe13, and UBe13 in the temperature range between 7 and
300 K in order to investigate their crystallographic characteristics
systematically. They keep the NaZn13-type cubic structure down to the lowest
temperature. We estimated their Debye temperature to be 600 - 750 K from
analyses of the temperature dependence of a lattice parameter, being in good
agreement with the values reported previously. Rietveld refinements on the
obtained powder patterns revealed that the M atom in the 8a site is located in
an almost ideal snub cube formed by 24 Be atoms in the 96i site, whose caged
structure is unchanged even at the low temperatures. In addition, it is argued
from the temperature variation of an isotropic mean-square displacement
parameter that the MBe13 compounds commonly have a low-energy phonon mode,
which can be described by a model assuming an Einstein oscillation of the M
atom with a characteristic temperature of ~ 160 K.Comment: 8 pages with 6 figures and 2 table
Magnetic Properties of YbBe13 Probed by Neutron Scattering and Thermodynamic Measurements
We examined the magnetic properties of YbBe13, which exhibits an
antiferromagnetic order below TN = 1.2 K. Unlike other MBe13 compounds (M =
rare earth/actinide elements), based on elastic neutron scattering, we observed
an incommensurate magnetic propagation vector {\tau} = (0,0,{\tau}z), where
{\tau}z = 0.5385 is in the reciprocal lattice unit. Additionally, we
constructed a precise magnetic phase diagram for YbBe13. We observed
non-trivial magnetic anomalies in YbBe13, which cannot be understood based on a
simple helical order. Our results for YbBe13 provide an opportunity to
reconsider the electron state of UBe13 and present an important step toward a
comprehensive understanding of magnetic correlations in MBe13 series.Comment: 5 pages, 5 figure
Unconventional Strong Spin-Fluctuation Effects around the Critical Pressure of the Itinerant Ising-Type Ferromagnet URhAl
Resistivity measurements were performed for the itinerant Ising-type
ferromagnet URhAl at temperatures down to 40 mK under high pressure up to 7.5
GPa, using single crystals. We found that the critical pressure of the Curie
temperature exists at around ~ 5.2 GPa. Near , the -coefficient
of the Fermi-liquid resistivity term below is largely enhanced
with a maximum around 5.2-5.5 GPa. Above , the exponent of the resistivity
deviates from 2. At , it is close to , which is
expected by the theory of three-dimensional ferromagnetic spin fluctuations for
a 2nd-order quantum-critical point (QCP). However, disappears as a
1st-order phase transition, and the critical behavior of resistivity in URhAl
cannot be explained by the theory of a 2nd-order QCP. The 1st-order nature of
the phase transition is weak, and the critical behavior is still dominated by
the spin fluctuation at low temperature. With increasing pressure, the
non-Fermi-liquid behavior is observed in higher fields. Magnetic field studies
point out a ferromagnetic wing structure with a tri-critical point (TCP) at ~
4.8-4.9 GPa in URhAl. One open possibility is that the switch from the
ferromagnetic to the paramagnetic states does not occur simply but an
intermediate state arises below the TCP as suggested theoretically recently.
Quite generally, if a drastic Fermi-surface change occurs through , the
nature of the interaction itself may change and lead to the observed
unconventional behavior.Comment: 9 pages, 9 figure
Orientation of point nodes and nonunitary triplet pairing tuned by the easy-axis magnetization in UTe2
The gap structure of a novel uranium-based superconductor UTe, situated
in the vicinity of ferromagnetic quantum criticality, has been investigated via
specific-heat measurements in various field orientations. Its
angular variation shows a characteristic shoulder anomaly
with a local minimum in at moderate fields rotated within the
and planes. Based on the theoretical calculations, these features can
be attributed to the presence of point nodes in the superconducting gap along
the direction. Under the field orientation along the easy-magnetization
axis, an unusual temperature dependence of the upper critical field at low
fields together with a convex downward curvature in were observed. These
anomalous behaviors can be explained on the basis of a nonunitary triplet state
model with equal-spin pairing whose is tuned by the magnetization
along the axis. From these results, the gap symmetry of UTe is most
likely described by a vector order parameter of .Comment: 6 pages, 4 figures (main text) + 7 pages, 5 figures (Supplementary
Material), accepted for publication in Phys. Rev. Researc
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