61 research outputs found
Macroscopic Quantum Tunneling in Small Antiferromagnetic Particles: Effects of a Strong Magnetic Field
We consider an effect of a strong magnetic field on the ground state and
macroscopic coherent tunneling in small antiferromagnetic particles with
uniaxial and biaxial single-ion anisotropy. We find several tunneling regimes
that depend on the direction of the magnetic field with respect to the
anisotropy axes. For the case of a purely uniaxial symmetry and the field
directed along the easy axis, an exact instanton solution with two different
scales in imaginary time is constructed. For a rhombic anisotropy the effect of
the field strongly depends on its orientation: with the field increasing, the
tunneling rate increases or decreases for the field parallel to the easy or
medium axis, respectively. The analytical results are complemented by numerical
simulations.Comment: 11 pages, 6 figure
First- and second-order transitions of the escape rate in ferrimagnetic or antiferromagnetic particles
Quantum-classical escape-rate transition has been studied for two general
forms of magnetic anisotropy in ferrimagnetic or antiferromagnetic particles.
It is found that the range of the first-order transition is greatly reduced as
the system becomes ferrimagnetic and there is no first-order transition in
almost compensated antiferromagnetic particles. These features can be tested
experimentally in nanomagnets like molecular magnets.Comment: 11 pages, 3 figures, to appear in Europhys. Let
Probing the dynamics of quasicrystal growth using synchrotron live imaging
The dynamics of quasicrystal growth remains an unsolved problem in condensed
matter. By means of synchrotron live imaging, facetted growth proceeding by the
tangential motion of ledges at the solid-melt interface is clearly evidenced
all along the solidification of icosahedral AlPdMn quasicrystals. The effect of
interface kinetics is significant so that nucleation and free growth of new
facetted grains occur in the melt when the solidification rate is increased.
The evolution of these grains is explained in details, which reveals the
crucial role of aluminum rejection, both in the poisoning of grain growth and
driving fluid flow
Chirality tunneling in mesoscopic antiferromagnetic domain walls
We consider a domain wall in the mesoscopic quasi-one-dimensional sample
(wire or stripe) of weakly anisotropic two-sublattice antiferromagnet, and
estimate the probability of tunneling between two domain wall states with
different chirality. Topological effects forbid tunneling for the systems with
half-integer spin S of magnetic atoms which consist of odd number of chains N.
External magnetic field yields an additional contribution to the Berry phase,
resulting in the appearance of two different tunnel splittings in any
experimental setup involving a mixture of odd and even N, and in oscillating
field dependence of the tunneling rate with the period proportional to 1/N.Comment: 4 pages + 2 figures, references correcte
Mirror duality and noncommutative tori
In this paper, we study a mirror duality on a generalized complex torus and a
noncommutative complex torus. First, we derive a symplectic version of Riemann
condition using mirror duality on ordinary complex tori. Based on this we will
find a mirror correspondence on generalized complex tori and generalize the
mirror duality on complex tori to the case of noncommutative complex tori.Comment: 22pages, no figure
Macroscopic quantum coherence in mesoscopic ferromagnetic systems
In this paper we study the Macroscopic Quantum Oscillation (MQO) effect in
ferromagnetic single domain magnets with a magnetic field applied along the
hard anistropy axis. The level splitting for the ground state, derived with the
conventional instanton method, oscillates with the external field and is
quenched at some field values. A formula for quantum tunneling at excited
levels is also obtained. The existence of topological phase accounts for this
kind of oscillation and the corresponding thermodynamical quantities exhibit
similar interference effects which resembles to some extent the electron
quantum phase interference induced by gauge potential in the Aharonov-Bohm
effect and the -vacuum in Yang-Mills field theory..Comment: 12 pages, 4 figures, to appear in Phys. Rev.
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