269 research outputs found
Magnetic Properties of the Spin-1/2 Deformed Kagome Antiferromagnet Edwardsite
We prepared a powder sample of edwardsite Cd2Cu3(SO4)2(OH)6 4H2O, which is a
new candidate compound for the spin-1/2 kagome antiferromagnet, and studied its
magnetic properties by magnetic susceptibility and heat capacity measurements.
Edwardsite has a deformed kagome lattice with an average antiferromagnetic
interaction of 51 K between nearby spins and shows an antiferromagnetic order
accompanied by a small ferromagnetic moment below 4.3 K. The weak
ferromagnetism is likely due to spin canting caused by sizable
Dzyaloshinsky-Moriya interactions, which may stabilize the long-range magnetic
order instead of a spin-liquid state expected for the kagome antiferromagnet.Comment: 5 pages, 6 figures, accepted for publication in J. Phys. Soc. Jp
Line-Node Dirac Semimetal and Topological Insulating Phase in Noncentrosymmetric Pnictides CaAgX (X = P, As)
Two noncentrosymmetric ternary pnictides, CaAgP and CaAgAs, are reported as
topological line-node semimetals protected solely by mirror-reflection
symmetry. The band gap vanishes on a circle in momentum space, and surface
states emerge within the circle. Extending this study to spin-orbit coupled
systems reveals that, compared with CaAgP, a substantial band gap is induced in
CaAgAs by large spin-orbit interaction. The resulting states are a topological
insulator, in which the Z2 topological invariant is given by 1; 000. To clarify
the Z2 topological invariants for time-reversal-invariant systems without
spatial-inversion symmetry, we introduce an alternative way to calculate the
invariants characterizing a line node and topological insulator for
mirror-reflection-invariant systems.Comment: 4+4 pages, 3+3 figure
Magnetic Order in the Spin-1/2 Kagome Antiferromagnet Vesignieite
We report results of magnetic susceptibility and 51V- and 63,65Cu-NMR
measurements on a high-quality powder sample of vesignieite BaCu3V2O8(OH)2, a
candidate for the spin-1/2 kagome antiferromagnet. We observed a twostep
magnetic transition: the appearance of spatially inhomogeneous static moments
below 13 K and a long-range order below 9 K. The NMR data indicate a Q = 0
magnetic structure at 1.4 K with the in-plane spin components of three
sublattices oriented at nearly 120 degrees to each other and the magnitude of
the ordered moments of at least 0.6 muBComment: 5 pages, 5 figure
Spin-Liquid State in the S = 1/2 Hyperkagome Antiferromagnet Na4Ir3O8
A spinel related oxide, Na4Ir3O8, was found to have a three dimensional
network of corner shared Ir4+ (t2g^5) triangles. This gives rise to an
antiferromagnetically coupled S = 1/2 spin system formed on a geometrically
frustrated hyperkagome lattice. Magnetization M and magnetic specific heat Cm
data showed the absence of long range magnetic ordering at least down to 2 K.
The large Cm at low temperatures is independent of applied magnetic field up to
12 T, in striking parallel to the behavior seen in triangular and kagome
antiferromagnets reported to have a spin-liquid ground state. These results
strongly suggest that the ground state of Na4Ir3O8 is a three dimensional
manifestation of a spin liquid.Comment: 4 pages, 4 figure
Distorted Kagome Lattice Generated by a Unique Orbital Arrangement in the Copper Mineral KCu3As2O7(OH)3
We study polycrystalline samples of KCu3As2O7(OH)3, a new candidate spin-1/2
kagome antiferromagnet, by magnetic susceptibility and heat capacity
measurements above 2 K. The unique arrangement of the 3z2 - r2 and x2 - y2
orbitals on the Cu2+ kagome net is noted and compared to the orbital patterns
found in other kagome minerals. It is suggested that this orbital arrangement
gives rise to one antiferromagnetic and two ferromagnetic interactions on
isosceles triangles forming a highly distorted kagome lattice. KCu3As2O7(OH)3
is found to show an antiferromagnetic long-range order at T_N = 7.2 K.
Remarkably, a spin entropy is more gradually released upon cooling below T_N
compared with a conventional magnetic long-range order, which may originate
from the geometrical frustration still present in this highly distorted kagome
lattice.Comment: 5 pages, 4 figure
Collinear Spin-density-wave Order and Anisotropic Spin Fluctuations in the Frustrated -- Chain Magnet NaCuMoO(OH)
The phase diagram of the quasi-one-dimensional magnet NaCuMoO(OH) is
established through single-crystal NMR and heat-capacity measurements. The
Na and H NMR experiments indicate a spiral and a collinear
spin-density-wave (SDW) order below and above = 1.5-1.8 T, respectively.
Moreover, in the paramagnetic state above the SDW transition temperature, the
nuclear spin-lattice relaxation rate indicates anisotropic spin
fluctuations that have gapped excitations in the transverse spectrum but
gapless ones in the longitudinal spectrum. These static and dynamic properties
are well described by a theoretical model assuming quasi-one-dimensional chains
with competing ferromagnetic nearest-neighbor interactions and
antiferromagnetic next-nearest-neighbor interactions (-
chains). Because of the excellent crystal quality and good one dimensionality,
NaCuMoO(OH) is a promising compound to elucidate the unique physics of the
frustrated - chain.Comment: accepted for publication in Physical Review
YCr6Ge6 as a Candidate Compound for a Kagome Metal
We show that YCr6Ge6, comprising a kagome lattice made up of Cr atoms, is a
plausible candidate compound for a kagome metal that is expected to exhibit
anomalous phenomena such as flat-band ferromagnetism. Resistivity,
magnetization, and heat capacity are measured on single crystals of YCr6Ge6,
and band structure calculations are performed to investigate the electronic
structure. Curie-Weiss-like behavior in magnetic susceptibility, T2 dependence
in resistivity, and a Sommerfeld coefficient doubly enhanced from a calculated
value indicate a moderately strong electron correlation. Interestingly, the
in-plane resistivity is twice as large as the interplane resistivity, which is
contrary to the simple expectation from the layered structure. Band structure
calculations demonstrate that there are partially flat bands slightly below the
Fermi level near the {\Gamma} point, which is ascribed to Cr 3d3z2-r2 bands and
may govern the properties of this compound.Comment: 14 page
Large Diamagnetism of AV2Al20 (A = Y and La)
We find anomalously large diamagnetic responses in the cage compounds AV2Al20
where A = Y and La, not A = Al0.3, Sc0.4, and Lu, despite the apparent
similarities in crystal and electronic structures among these compounds. The
magnetic susceptibilities of the Y and La compounds become -1.94 and -7.44 x
10-4 cm3 mol-1 at 10 K, respectively, the latter of which corresponds to
approximately one-quarter of that of bismuth, a well-known diamagnetic
material, in terms of unit volume. The origin is not clear but may be related
to a specific evolution in the band structure, as the diamagnetic response
increases with increasing lattice constant.Comment: 5 pages, 4 figures, 1 table; to pe published in J. Phys. Soc. Jp
Rattling and Superconducting Properties of the Cage Compound GaxV2Al20
Low-energy rattling modes and their effects on superconductivity are studied
in the cage compound GaxV2Al20. A series of polycrystalline samples of 0 < x =<
0.6 are examined through resistivity, magnetic susceptibility, and heat
capacity measurements. A weak-coupling BCS superconductivity is observed below
Tc = 1.4-1.7 K for all the samples. For small Ga contents below 0.20,
approximately 30% of the cages are occupied by rattling Al atoms having an
Einstein temperature TE of 23 K, probably with most Ga atoms substituting for
the cage-forming Al atoms. For higher Ga contents, approximately 0.05 Ga and
0.25-0.35 Al atoms coexist statistically inside the cages and behave as
rattlers with TE ~ 8 and 23 K, respectively. A significant effect of Ga
rattling on the superconductivity is clearly evidenced by the observation of a
sharp rise in Tc by 8% at x = 0.20 when 0.05 Ga atoms are introduced into the
case. Probably, the electron-phonon interaction is significantly enhanced by an
additional contribution to the phonon density of states from the extremely low
energy rattling modes of Ga atoms. In addition, a large softening of the
acoustic modes is observed for x => 0.20, suggesting that the cage itself
becomes anomalously soft in the presence of low-energy Ga rattling modes.Comment: 13 pages, 16 figures, 1 table; J. Phys. Soc. Jpn, in pres
Crossing-Line-Node Semimetals: General Theory and Application to Rare-Earth Trihydrides
Multiple line nodes in energy-band gaps are found in semimetals preserving
mirror-reflection symmetry. We classify possible configurations of multiple
line nodes with crossing points (crossing line nodes) under point-group
symmetry. Taking the spin-orbit interaction (SOI) into account, we also
classify topological phase transitions from crossing-line-node Dirac semimetals
to other topological phases, e.g., topological insulators and point-node
semimetals. This study enables one to find crossing-line-node semimetal
materials and their behavior in the presence of SOI from the band structure in
the absence of SOI without detailed calculations. As an example, the theory
applies to hexagonal rare-earth trihydrides with the HoD3 structure and
clarifies that it is a crossing-line-node Dirac semimetal hosting three line
nodes.Comment: 16 pages, 9 figure
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