228 research outputs found
Magnetization plateau and incommensurate spin modulation in Ca3Co2O6
The magnetic properties of a trigonal prism unit of the spin-2 frustrated
compound Ca3Co2O6 are studied by means of the density-matrix renormalization
group method. A magnetization plateau at ( is the saturation
magnetization) with ferrimagnetic structure is observed. By fitting the
experimental data of magnetic curve, an estimation of the couplings gives
J1=-26.84K, J_{2}=0.39K, and J_{3}=0.52K. The local magnetic moments are
unveiled to exhibit an incommensurate sinusoidally modulation along the three
chains of the trigonal prism, which gives a strong theoretical support to the
experimentally observed incommensurate partially disordered antiferromagnetic
state for Ca3Co2O6. The present result suggests that the modulation indeed
originates from the competition of antiferromagnetic and ferromagnetic
couplings.Comment: 4 pages, 4 figures, accepted by Appl. Phys. Lett
Quantum Phase Transition, O(3) Universality Class and Phase Diagram of Spin-1/2 Heisenberg Antiferromagnet on Distorted Honeycomb Lattice: A Tensor Renormalization Group Study
The spin-1/2 Heisenberg antiferromagnet on the distorted honeycomb (DHC)
lattice is studied by means of the tensor renormalization group method. It is
unveiled that the system has a quantum phase transition of second-order between
the gapped quantum dimer phase and a collinear Neel phase at the critical point
of coupling ratio \alpha_{c} = 0.54, where the quantum critical exponents \nu =
0.69(2) and \gamma = 1.363(8) are obtained. The quantum criticality is found to
fall into the O(3) universality class. A ground-state phase diagram in the
field-coupling ratio plane is proposed, where the phases such as the dimer,
semi-classical Neel, and polarized phases are identified. A link between the
present spin system to the boson Hubbard model on the DHC lattice is also
discussed.Comment: 6 pages, 5 figures, published in Phys. Rev.
Phase transitions and thermodynamics of the two-dimensional Ising model on a distorted Kagom\'{e} lattice
The two-dimensional Ising model on a distorted Kagom\'{e} lattice is studied
by means of exact solutions and the tensor renormalisation group (TRG) method.
The zero-field phase diagrams are obtained, where three phases such as
ferromagnetic, ferrimagnetic and paramagnetic phases, along with the
second-order phase transitions, have been identified. The TRG results are quite
accurate and reliable in comparison to the exact solutions. In a magnetic
field, the magnetization (), susceptibility and specific heat are studied by
the TRG algorithm, where the plateaux are observed in the magnetization
curves for some couplings. The experimental data of susceptibility for the
complex Co(N)(bpg) DMF are fitted with the TRG results,
giving the couplings of the complex and
Design of Wind Turbine Vibration Monitoring System
In order to ensure safety of wind turbine operation and to reduce the occurrence of faults as well as to improve the reliability of wind turbine operation, a vibration monitoring for wind turbine is developed. In this paper, it analyses the enlargement of all the parts of the structure and the working mechanism, the research method of wind turbine operation vibration is introduced, with the focus being the use of the sensor principle. Finally the hardware design and software of this system is introduced and the main function of this system is described, which realizes condition monitoring of the work state of wind turbines
Thermodynamics of spin-1/2 tetrameric Heisenberg antiferromagnetic chain
The thermodynamic properties of a spin S=1/2 tetrameric Heisenberg
antiferromagnetic chain with alternating interactions AF1-AF2-AF1-F (AF and F
denote the antiferromagnetic and ferromagnetic couplings, respectively) are
studied by means of the transfer-matrix renormalization group method and
Jordan-Wigner transformation. It is found that in the absence of magnetic
field, the thermodynamic behaviors are closely related to the gapped low-lying
excitations, and a novel structure with three peaks in the temperature
dependence of specific heat is unveiled. In a magnetic field, a phase diagram
in the temperature-field plane for the couplings satisfying JAF1=JAF2=JF is
obtained, in which various phases are identified. The temperature dependence of
thermodynamic quantities including the magnetization, susceptibility and
specific heat are studied to characterize the corresponding phases. It is
disclosed that the magnetization has a crossover behavior at low temperature in
the Luttinger liquid phase, which is shown falling into the same class as that
in the S=1 Haldane chain. In the plateau regime, the thermodynamic behaviors
alter at a certain field, which results from the crossing of two excitation
spectra. By means of the fermion mapping, it is uncovered that the system has
four spectra from fermion and hole excitations that are responsible for the
observed thermodynamic behaviors.Comment: 10 pages, 10 figures, accepted by Phys. Rev.
Emergent spin-1 trimerized valence bond crystal in the spin-1/2 Heisenberg model on the star lattice
We explore the frustrated spin- Heisenberg model on the star lattice
with antiferromagnetic (AF) couplings inside each triangle and ferromagnetic
(FM) inter-triangle couplings (), and calculate its magnetic and
thermodynamic properties. We show that the FM couplings do not sabotage the
magnetic disordering of the ground state due to the frustration from the AF
interactions inside each triangle, but trigger a fully gapped
inversion-symmetry-breaking trimerized valence bond crystal (TVBC) with
emergent spin-1 degrees of freedom. We discover that with strengthening ,
the system scales exponentially, either with or without a magnetic field :
the order parameter, the five critical fields that separate the -
ground-state phase diagram into six phases, and the excitation gap obtained by
low-temperature specific heat, all depend exponentially on . We calculate
the temperature dependence of the specific heat, which can be directly compared
with future experiments.Comment: 7 pages, 6 figure
Linearized Tensor Renormalization Group Algorithm for Thermodynamics of Quantum Lattice Models
A linearized tensor renormalization group (LTRG) algorithm is proposed to
calculate the thermodynamic properties of one-dimensional quantum lattice
models, that is incorporated with the infinite time-evolving block decimation
technique, and allows for treating directly the two-dimensional transfer-matrix
tensor network. To illustrate its feasibility, the thermodynamic quantities of
the quantum XY spin chain are calculated accurately by the LTRG, and the
precision is shown to be comparable with (even better than) the transfer matrix
renormalization group (TMRG) method. Unlike the TMRG scheme that can only deal
with the infinite chains, the present LTRG algorithm could treat both finite
and infinite systems, and may be readily extended to boson and fermion quantum
lattice models.Comment: published versio
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