46 research outputs found
Magnetic phase diagram of the strongly frustrated quantum spin chain system PbCuSO(OH) in tilted magnetic fields
We report the phase diagram of strongly frustrated
anisotropic spin chain material linarite PbCuSO(OH) in tilted magnetic
fields up to 10 T and temperatures down to 0.2 K. By means of torque
magnetometry we investigate the phase diagram evolution as the magnetic field
undergoes rotation in and planes. The key
finding is the robustness of the high field spin density wave-like phase, which
may persist even as the external field goes orthogonal to the chain direction
. In contrast, the intermediate collinear antiferromagnetic phase
collapses at moderate deflection angles with respect to axis.Comment: 7 pages, 9 figure
Thermodynamics of a frustrated quantum magnet on a square lattice
We report the magnetic and calorimetric measurements in single crystal
samples of the square lattice quantum antiferromagnet
BaCdVO(PO). An investigation of the scaling of magnetization reveals a
"dimensionality reduction" indicative of a strong degree of geometric
frustration. Below a characteristic temperature of ~mK we
observe the emergence of an additional strongly fluctuating quantum phase close
to full magnetic saturation. It is separated from the magnetically ordered
state by first- and second-order phase transitions, depending on the
orientation of the applied magnetic field. We suggest that this phase may
indeed be related to the theoretically predicted spin-nematic state.Comment: 10 pages, 9 figure
Spin waves near the edge of halogen substitution induced magnetic order in Ni(ClBr)4SC(NH)
We report an inelastic neutron scattering study of magnetic excitations in a
quantum paramagnet driven into a magnetically ordered state by chemical
substitution, namely Ni(ClBr)4SC(NH) with
. The measured spectrum is well accounted for by the generalized
spin wave theory (GSWT) approach [M. Matsumoto and M. Koga, [J. Phys. Soc. Jap.
76, 073709 (2007)]. This analysis allows us to determine the effective
Hamiltonian parameters for a direct comparison with those in the previously
studied parent compound and `underdoped' system. The issue of magnon lifetimes
due to structural disorder is also addressed.Comment: 8 pages, 7 figure
Switching of anisotropy and phase diagram of a Heisenberg square lattice S=1/2 antiferromagnet Cu(pz)2(ClO4)2
Experiments in the antiferromagnetic phase of a quasi 2D quasi-square
lattice antiferromagnet Cu(pz)2(ClO4)2 reveal a biaxial type of the anisotropy,
instead of the easy-plane one, considered before. The weak in-plane anisotropy,
found by means of electron spin resonance spectroscopy and magnetization
measurements, is about an order of magnitude weaker, than the off-plane
anisotropy. The weak in-plane anisotropy results in a spin-flop phase
transition for the magnetic field aligned along easy axis, and, thereby, in a
bicritical point on the phase diagram. A remarkable feature of the weak
in-plane anisotropy is the abrupt change of its sign at the spin-flop point.
This anisotropy switching disappears at the tilting of magnetic field to the
easy axis by the angle of 10 within the plane. The nature of the abrupt
anisotropy reversal remains unclear. The phase diagram is characterized by the
increase of the ordering temperature in the magnetic field used, except for a
dip near the bicritical point.Comment: 14 pages, 22 figure
Giant dielectric nonlinearities at a magnetic Bose-Einstein condensation
We experimentally investigate the dielectric response of the low-dimensional
gapped quantum magnet CuClHCSO near a magnetic
field-induced quantum critical point, which separates the quantum-disordered
and helimagnetic ground states. The observed magnetocapacitive effect
originates from an improper ferroelectric nature of the transition, which
itself is perhaps one of the best known realizations of Bose--Einstein
condensation of magnons. Despite that, we find that the magnetocapacitive
effect associated with the transition exhibits huge and very unusual
anharmonicities.Comment: 7 pages, 8 figure
Scaling of temporal correlations in an attractive Tomonaga-Luttinger spin liquid
We report temperature-dependent neutron scattering measurements of the local
dynamic structure factor in the quantum spin ladder
(CHN)CuBr in a magnetic field ~T, in its gapless
quantum-critical phase. We show that the measured quantity has a scaling form
consistent with expectations for a Tomonaga-Luttinger liquid with attraction.
The measured Luttinger parameter and scaling function are in
excellent agreement with density matrix renormalization group numerical
calculations for the underlying spin Hamiltonian.Comment: 5 pages, 3 figure
Magnetic resonance in the ordered phases of the 2D frustrated quantum magnet Cs2CuCl4
The temperature evolution of the electron spin resonance is studied at
cooling the crystal samples of Cs2CuCl4 through the Neel point 0.62 K. A
coexistence of the high-frequency spinon type resonance developed in the
spin-liquid phase and of the low-frequency antiferromagnetic resonance was
found in the ordered phase. The low-frequency magnetic resonance spectrum in
the low field range has two gapped branches and corresponds well to the
spectrum of spin excitations of a planar spiral spin structure with two axes of
the anisotropy. The field induced phase transitions result in a more
complicated low-frequency spectra.Comment: 10 pages, 17 figure
Dynamics of a bond-disordered quantum magnet near criticality
Neutron scattering is used to study
NiClBr4SC(NH), , a bond-disordered
modification of the well-known gapped antiferromagnetic quantum spin
system NiCl4SC(NH). The magnetic excitation spectrum
throughout Brillouin zone is mapped out at mK using high-resolution
time-of-flight spectroscopy. It is found that the dispersion of spin excitation
is renormalized, as compared to that in the parent compound. The lifetime of
excitations near the bottom of the band is substantially decreased. No
localized states are found below the gap energy meV. At the
same time, localized zero wave vector states are detected above the top of the
band. The results are consistent with a more or less continuous random
distribution of bond strengths, and a discrete, possibly bimodal, distribution
of single-ion anisotropies in the disordered material.Comment: 11 pages, 10 figures, 3 table
Magnetic phase diagram of the linear quantum ferro-antiferromagnet CsCuMoO
A single-crystal sample of the frustrated quasi one-dimensional quantum
magnet CsCuMoO is investigated by magnetic and
thermodynamic measurements.A combination of specific heat and magnetic torque
measurements maps out the entire - phase diagram for three
orientations.Remarkably, a new phase emerges below the saturation field,
irrespective of the crystal orientation. It is suggested that the presaturation
phase represents spin-nematic order or other multi-magnon condensate. The phase
diagrams within the long-range ordered dome are qualitatively different for
each geometry. In particular, multiple transitions are identified in the field
along the chain direction
Spin gap in a quasi-1D S=1/2 antiferromagnet K2CuSO4Cl2
Electron spin resonance experiments in the quasi-1D S=1/2 antiferromagnet
KCuSOCl reveal opening of a gap in absence of magnetic ordering, as
well as an anisotropic shift of the resonance magnetic field. These features of
magnetic excitation spectrum are explained by a crossover between a gapped
spinon-type doublet ESR formed in a 1D antiferromagnet with uniform
Dzyaloshinskii-Moriya interaction and a Larmor-type resonance of a quasi-1D
Heisenberg systemComment: 9 pages, 12 figure