175 research outputs found
Magnetic-field- and pressure-induced quantum phase transition in CsFeCl proved via magnetization measurement
We have performed magnetization measurements of the gapped quantum magnet
CsFeCl at temperatures () down to 0.5\,K at ambient pressure and down to
1.8\,K at hydrostatic pressures () of up to 1.5\,GPa. The lower-field ()
phase boundary of the field-induced ordered phase at ambient pressure is found
to follow the power-law behavior expressed by the formula \,\,\,\,. The application of
pressure extends the phase boundary to both a lower field and higher
temperature. Above the critical pressure \,\,0.9\,GPa, the
transition field associated with the excitation gap becomes zero,
and a signature of the magnetic phase transition is found in the -dependence
of magnetization in a very low applied field. This suggests that CsFeCl
exhibits a pressure-induced magnetic phase transition at .Comment: 8 pages, 8 figures, to appear in Phys. Rev.
Experimental Verification of the Universality of Magnetic-Field-Induced Bose-Einstein Condensation of Magnons
CsFeBr is an hexagonal antiferromagnet that has a singlet
ground state owing to its large easy-plane single-ion anisotropy. The critical
behavior of the magnetic-field-induced phase transition for a magnetic field
parallel to the axis, which can be described by the Bose-Einstein
condensation (BEC) of magnons under the symmetry, was investigated via
magnetization and specific heat measurements down to 0.1K. For the specific
heat measurement, we have developed a method of effectively suppressing the
torque acting on a sample with strong anisotropy that uses the spin dimer
compound BaCoSiOCl with large and anisotropic Van Vleck
paramagnetism. The temperature dependence of the transition field was found to follow the power-law with a critical exponent of
and critical field of
T. This result verifies the universality of the three-dimensional BEC of
magnons described by .Comment: 5 pages, 3 figures, to appear in Phys. Rev.
Strong Suppression of Magnetic Ordering in an S = 1/2 Square-Lattice Heisenberg Antiferromagnet Sr2CuTeO6
We report the magnetic susceptibility and the low-temperature specific heat
of a double perovskite compound, Sr2CuTeO6, which is expected as the spin-1/2
square-lattice Heisenberg antiferromagnet with nearest-neighbor J1 and
next-nearest-neighbor J2 exchange interactions. The specific heat exhibits a
sharp lambda-like anomaly at TN = 4.8 K indicative of magnetic ordering, which
is much lower than those in isostructural A2CuMO6 with A = Ba, Sr and M = W,
Mo. This indicates the strong suppression of magnetic ordering in Sr2CuTeO6. We
estimate the exchange constant J1/kB ~ 80 K and J2/J1 < 0.07 from magnetic
susceptibility data using Pade approximation of high temperature expansion and
quantum Monte Carlo method. The strong suppression of magnetic ordering in
Sr2CuTeO6 should be ascribed to the weekness of the interlayer exchange.Comment: 3 pages, 3 Figures, to appear in J. Phys. Soc. Jp
Quantum phase transition between disordered and ordered states in the spin-1/2 kagome lattice antiferromagnet (RbCs)CuSnF
We have systematically investigated the variation of the exchange parameters
and the ground state in the kagome-lattice antiferromagnet
(RbCs)CuSnF, via magnetic measurements using
single crystals. One of the parent compounds, RbCuSnF, which has
a distorted kagome lattice accompanied by four sorts of nearest-neighbor
exchange interaction, has a disordered ground state described by a pinwheel
valence-bond-solid state. The other parent compound, CsCuSnF,
which has a uniform kagome lattice at room temperature, has an ordered ground
state with the = 0 spin structure. The analysis of magnetic
susceptibilities shows that with increasing cesium concentration , the
exchange parameters increase with the tendency to be uniform. It was found that
the ground state is disordered for 0.53. The
pseudogap observed for 0.53
approach zero at 0.53. This is indicative of the
occurrence of a quantum phase transition at .Comment: 8 pages, 8 figures, to appear in Phys. Rev.
Magnetic Phase Diagram of the S=1/2 Triangular-Lattice Heisenberg Antiferromagnet Ba3CoNb2O9
We report the results of low-temperature thermal and magnetic measurements on
BaCoNbO powder, described as a uniform triangular-lattice
antiferromagnet (TLAF) with a fictitious spin-1/2. BaCoNbO is found
to undergo two-step antiferromagnetic transitions at
and . As the magnetic field is increased, both and monotonically decrease. The magnetic field vs temperature
phase diagram indicates that the exchange interactions are nearly of the
Heisenberg type with weak easy-axis anisotropy and that the exchange
interaction between triangular lattices is crucial, in contrast to the case of
the quasi-two-dimensional TLAF BaCoSbO [Susuki {\it et al}., Phys.
Rev. Lett. \textbf{110}, 267201 (2013)].Comment: 14 pages, 6 Figures, to appear in Phys. Rev.
Quasi-two-dimensional Bose-Einstein condensation of lattice bosons in spin-1/2 XXZ ferromagnet KCuF
KCuF is magnetically described as a spin-1/2, quasi-two-dimensional
(2D), square-lattice XXZ ferromagnet with weak easy-plane anisotropy. The
magnetic ordering for an applied magnetic field parallel to the axis is
equivalent to the Bose\,--\,Einstein condensation (BEC) of lattice bosons, as
discussed by Matsubara and Matsuda [Prog. Theor. Phys. \textbf{16}, 569
(1956)]. Magnetization and specific heat measurements were performed to obtain
the temperature vs magnetic field phase diagram for . The
phase boundary between polarized and ordered phases was found to be expressed
by the power law with
exponent in a wide temperature range, in agreement with
the theory of quasi-2D BEC.Comment: 5 pages, 4 figures, accepted for publication in Physics. Rev.
Field-driven successive phase transitions in quasi-two-dimensional frustrated antiferromagnet BaCoTeO and highly degenerate classical ground states
We report the results of magnetization and specific heat measurements of
BaCoTeO composed of two subsystems A and B, which are magnetically
described as an triangular-lattice Heisenberg-like
antiferromagnet and a honeycomb-lattice Ising-like antiferromagnet,
respectively. These two subsystems were found to be approximately decoupled.
BaCoTeO undergoes magnetic phase transitions at
K and K, which can be interpreted as the orderings of
subsystems B and A, respectively. Subsystem A exhibits a magnetization plateau
at one-third of the saturation magnetization for the magnetic field
perpendicular to the axis owing to the quantum order-by-disorder, whereas
for , subsystem B shows three-step metamagnetic transitions
with magnetization plateaus at zero, one-third and one-half of the saturation
magnetization. The analysis of the magnetization process for subsystem B shows
that the classical ground states at these plateaus are infinitely degenerate
within the Ising model.Comment: 7 pages, 8 figure
Valence-Bond-Glass State with Singlet Gap in the Spin-1/2 Square-Lattice Random - Heisenberg Antiferromagnet SrCuTeWO
The double-perovskite compounds SrCuTeO and SrCuWO are
magnetically described as quasi-two-dimensional spin-1/2 square-lattice
Heisenberg antiferromagnets with predominant and
exchange interactions, respectively. We report the low-temperature magnetic
properties of SrCuTeWO with randomness in the magnitudes of
and . It was found that the low-temperature specific heat for
has a large component proportional to the temperature
above 1.2 K, although the low-temperature specific heat for the two parent
systems is approximately proportional to . With decreasing temperature
below 1.2 K, the -linear component decreases rapidly toward zero, which is
insensitive to the magnetic field up to 9 T. This is suggestive of the singlet
excitation decoupled from the magnetic field. The NMR spectrum for
exhibits no long-range order down to 1.8 K. These results indicates that the
ground state of SrCuTeWO is a valence-bond-glass state with
singlet gaps.Comment: 6 pages, 5 figure
Magnetic Structure of the Quasi-Two-Dimensional Square-Lattice Heisenberg Antiferromagnet SrCuTeO
The magnetic structure of the double perovskite compound SrCuTeO was
determined from neutron powder diffraction data. This material is magnetically
described as an quasi-two-dimensional square-lattice Heisenberg
model with antiferromagnetic nearest-neighbor and next-nearest-neighbor
interactions. SrCuTeO undergoes a magnetic phase transition at K. The spin structure below is N\'{e}el
antiferromagnetic on the square lattice, which means that the nearest-neighbor
interaction () is stronger than the next-nearest-neighbor interaction
(), in contrast to other isostructural compounds such as BaCuWO
and SrCuWO, for which is realized.Comment: 6 pages, 7 figures, to appear in Phys. Rev.
Magnetization Process and Collective Excitations in the S=1/2 Triangular-Lattice Heisenberg Antiferromagnet Ba3CoSb2O9
We have performed high-field magnetization and ESR measurements on
BaCoSbO single crystals, as a representative two-dimensional
spin-1/2 Heisenberg antiferromagnet on a uniform triangular lattice, and have
determined all the magnetic parameters. For an applied magnetic field
parallel to the -plane, the entire magnetization curve including the
plateau at one-third of the saturation magnetization () is in
excellent agreement with the results of theoretical calculations except an
anomaly near , indicative of an additional field-induced
transition. However, for , the magnetization curve exhibits
a cusp near . Paramagnetic resonance signals above the N\'eel
temperature indicate the nearly isotropic -factor. A detailed analysis of
the collective ESR modes observed in the ordered state, combined with the
magnetization process, provides evidence of the weak easy-plane anisotropy.Comment: 5 pages, 4 figure
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