3,934 research outputs found
Analysis of fluctuations in the magnetic field obtained by IMP-2
Interplanetary magnetic field fluctuations from IMP 2 satellit
Demodulation of amplitude modulated RF WAVES in a plasma at resonance
Demodulation of amplitude modulated radio frequency waves in plasma at resonanc
Recent Progress in Spin Glasses
We review recent findings on spin glass models. Both the equilibrium
properties and the dynamic properties are covered. We focus on progress in
theoretical, in particular numerical, studies, while its relationship to real
magnetic materials is also mentioned.Comment: Chapter 6 in ``Frustrated Spin Systems'' edited by H.T.Die
Application of a continous time cluster algorithm to the Two-dimensional Random Quantum Ising Ferromagnet
A cluster algorithm formulated in continuous (imaginary) time is presented
for Ising models in a transverse field. It works directly with an infinite
number of time-slices in the imaginary time direction, avoiding the necessity
to take this limit explicitly. The algorithm is tested at the zero-temperature
critical point of the pure two-dimensional (2d) transverse Ising model. Then it
is applied to the 2d Ising ferromagnet with random bonds and transverse fields,
for which the phase diagram is determined. Finite size scaling at the quantum
critical point as well as the study of the quantum Griffiths-McCoy phase
indicate that the dynamical critical exponent is infinite as in 1d.Comment: 4 pages RevTeX, 3 eps-figures include
New technique for producing a strong multi-pole magnet
A new technique for producing strong multipole magnet is developed. A cylindrical magnet oriented with its easy axis of magnetization perpendicular to the cylinder axis is magnetized by a multipole magnetizer. This procedure results in a multipole magnet with a flux density almost sixty percent greater than the flux density produced by a multi-pole magnet which is not oriented. The technique is especially effective for producing small cylindrical magnets with many poles and agreement of a theoretical analysis with experimental results is very good, with deviations of no more than a few percent.</p
Quantum spin glass and the dipolar interaction
Systems in which the dipolar energy dominates the magnetic interaction, and
the crystal field generates strong anisotropy favoring the longitudinal
interaction terms, are considered. Such systems in external magnetic field are
expected to be a good experimental realization of the transverse field Ising
model. With random interactions this model yields a spin glass to paramagnet
phase transition as function of the transverse field. Here we show that the
off-diagonal dipolar interaction, although effectively reduced, destroys the
spin glass order at any finite transverse field. Moreover, the resulting
correlation length is shown to be small near the crossover to the paramagnetic
phase, in agreement with the behavior of the nonlinear susceptibility in the
experiments on \LHx. Thus, we argue that the in these experiments a
cross-over to the paramagnetic phase, and not quantum criticality, was
observed.Comment: To appear in Phys. Rev. Let
Numerical renormalization group study of random transverse Ising models in one and two space dimensions
The quantum critical behavior and the Griffiths-McCoy singularities of random
quantum Ising ferromagnets are studied by applying a numerical implementation
of the Ma-Dasgupta-Hu renormalization group scheme. We check the procedure for
the analytically tractable one-dimensional case and apply our code to the
quasi-one-dimensional double chain. For the latter we obtain identical critical
exponents as for the simple chain implying the same universality class. Then we
apply the method to the two-dimensional case for which we get estimates for the
exponents that are compatible with a recent study in the same spirit.Comment: 10 pages LaTeX, eps-figures and PTP-macros included. Proceedings of
the ICCP5, Kanazawa (Japan), 199
Spin-chirality decoupling in the one-dimensional Heisenberg spin glass with long-range power-law interactions
We study the issue of the spin-chirality decoupling/coupling in the ordering
of the Heisenberg spin glass by performing large-scale Monte Carlo simulations
on a one-dimensional Heisenberg spin-glass model with a long-range power-law
interaction up to large system sizes. We find that the spin-chirality
decoupling occurs for an intermediate range of the power-law exponent.
Implications to the corresponding -dimensional short-range model is
discussed.Comment: 5 pages, 4 figures, to appear in Physical Review Letter
Monte Carlo studies of the chiral and spin orderings of the three-dimensional Heisenberg spin glass
The nature of the ordering of the three-dimensional isotropic Heisenberg spin
glass with nearest-neighbor random Gaussian coupling is studied by extensive
Monte Carlo simulations. Several independent physical quantities are measured
both for the spin and for the chirality, including the correlation-length
ratio, the Binder ratio, the glass order parameter, the overlap distribution
function and the non-self-averageness parameter. By controlling the effect of
the correction-to-scaling, we have obtained a numerical evidence for the
occurrence of successive chiral-glass and spin-glass transitions at nonzero
temperatures, T_{CG} > T_{SG} > 0. Hence, the spin and the chirality are
decoupled in the ordering of the model. The chiral-glass exponents are
estimated to be \nu_{CG}=1.4+-0.2 and \eta_{CG}=0.6+-0.2, indicating that the
chiral-glass transition lies in a universality class different from that of the
Ising spin glass. The possibility that the spin and chiral sectors undergo a
simultaneous Kosterlitz-Thouless-type transition is ruled out. The chiral-glass
state turns out to be non-self-averaging, possibly accompanying a one-step-like
peculiar replica-symmetry breaking. Implications to the chirality scenario of
experimental spin-glass transitions are discussed.Comment: 20 pages, 24 figures. The Chi^2-analysis of the transition point has
been added with new Fig.12. Some references also adde
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