1,425 research outputs found
Spin tunneling properties in mesoscopic magnets: effects of a magnetic field
The tunneling of a giant spin at excited levels is studied theoretically in
mesoscopic magnets with a magnetic field at an arbitrary angle in the easy
plane. Different structures of the tunneling barriers can be generated by the
magnetocrystalline anisotropy, the magnitude and the orientation of the field.
By calculating the nonvacuum instanton solution explicitly, we obtain the
tunnel splittings and the tunneling rates for different angle ranges of the
external magnetic field ( and ). The
temperature dependences of the decay rates are clearly shown for each case. It
is found that the tunneling rate and the crossover temperature depend on the
orientation of the external magnetic field. This feature can be tested with the
use of existing experimental techniques.Comment: 27 pages, 4 figures, accepted by Euro. Phys. J.
Field-dependent quantum nucleation of antiferromagnetic bubbles
The phenomenon of quantum nucleation is studied in a nanometer-scale
antiferromagnet with biaxial symmetry in the presence of a magnetic field at an
arbitrary angle. Within the instanton approach, we calculate the dependence of
the rate of quantum nucleation and the crossover temperature on the orientation
and strength of the field for bulk solids and two-dimensional films of
antiferromagnets, respectively. Our results show that the rate of quantum
nucleation and the crossover temperature from thermal-to-quantum transitions
depend on the orientation and strength of the field distinctly, which can be
tested with the use of existing experimental techniques.Comment: 21 pages, 5 figures, Final version and accepted by Eur. Phys. J
The meson-exchange model for the interaction
In the present work, we apply the one-boson-exchange potential (OBEP) model
to investigate the possibility of Y(2175) and as bound states of
and respectively.
We consider the effective potential from the pseudoscalar -exchange and
-exchange, the scalar -exchange, and the vector
-exchange and -exchange. The and meson exchange
potential is repulsive force for the state and attractive for .
The results depend very sensitively on the cutoff parameter of the
-exchange () and least sensitively on that of the
-exchange (). Our result suggests the possible
interpretation of Y(2175) and as the bound states of
and respectively
Resonant quantum coherence of magnetization at excited states in nanospin systems with different crystal symmetries
The quantum interference effects induced by the Wess-Zumino term, or Berry
phase are studied theoretically in resonant quantum coherence of magnetization
vector between degenerate excited states in nanometer-scale single-domain
ferromagnets in the absence of an external magnetic field. By applying the
periodic instanton method in the spin-coherent-state path integral, we evaluate
the low-lying tunnel splittings between degenerate excited states of
neighboring wells. And the low-lying energy level spectrum of m-th excited
states are obtained with the help of the Bloch theorem in one-dimensional
periodic potential.Comment: 23 pages, final version and accepted by Eur. Phys. J.
Non-equilibrium dynamics of simple spherical spin models
We investigate the non-equilibrium dynamics of spherical spin models with
two-spin interactions. For the exactly solvable models of the d-dimensional
spherical ferromagnet and the spherical Sherrington-Kirkpatrick model the
asymptotic dynamics has for large times and for large waiting times the same
formal structure. In the limit of large waiting times we find in both models an
intermediate time scale, scaling as a power of the waiting time with an
exponent smaller than one, and thus separating the time-translation invariant
short-time dynamics from the aging regime. It is this time scale on which the
fluctuation-dissipation regime is violated. Aging in these models is similar to
that observed in spin glasses at the level of correlation functions, but
different at the level of response functions, and thus different at the level
of experimentally accessible quantities like the thermoremanent magnetization.Comment: 8 pages, 1 eps figur
Contribution of Continuum in the QCD Sum Rule for
Using the soft-pion theorem and the assumption on the final-state
interactions, we include the contribution of continuum into the QCD sum
rules for meson. We find that this contribution can
significantly lower the mass and the decay constant of state. For
the value of the current quark mass , we obtain the
mass of in the interval , being in agreement with the experimental data, and the vector
current decay constant of , much
lower than those obtained in previous literature
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