858 research outputs found
Self-organized patterns of macroscopic quantum tunneling in molecular magnets
We study low temperature resonant spin tunneling in molecular magnets induced
by a field sweep with account of dipole-dipole interactions. Numerical
simulations uncovered formation of self-organized patterns of the magnetization
and of the ensuing dipolar field that provide resonant condition inside a
finite volume of the crystal. This effect is robust with respect to disorder
and should be relevant to the dynamics of the magnetization steps observed in
molecular magnets.Comment: 4 Phys. Rev. pages, 5 figure
Renormalization of the tunnel splitting in a rotating nanomagnet
We study spin tunneling in a magnetic nanoparticle with biaxial anisotropy
that is free to rotate about its anisotropy axis. Exact instanton of the
coupled equations of motion is found that connects degenerate classical energy
minima. We show that mechanical freedom of the particle renormalizes magnetic
anisotropy and increases the tunnel splitting.Comment: 4 pages, 3 figure
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
Theory of magnetic deflagration
Theory of magnetic deflagration (avalanches) in crystals of molecular magnets
has been developed. The phenomenon resembles the burning of a chemical
substance, with the Zeeman energy playing the role of the chemical energy.
Non-destructive reversible character of magnetic deflagration, as well as the
possibility to continuously tune the flammability of the crystal by changing
the magnetic field, makes molecular magnets an attractive toy system for a
detailed study of the burning process. Besides simplicity, new features, as
compared to the chemical burning, include possibility of quantum decay of
metastable spin states and strong temperature dependence of the heat capacity
and thermal conductivity. We obtain analytical and numerical solutions for
criteria of the ignition of magnetic deflagration, and compute the ignition
rate and the speed of the developed deflagration front.Comment: 17 Pages, 17 Figure caption
Single magnetic molecule between conducting leads: Effect of mechanical rotations
We study spin-rotation effects in a magnetic molecule bridged between two
conducting leads. Dynamics of the total angular momentum couples spin tunneling
to the mechanical rotations. Landau-Zener spin transition produced by the
time-dependent magnetic field generates a unique pattern of mechanical
oscillations that can be detected by measuring the electronic tunneling current
through the molecule.Comment: 5 pages, 2 figure
On governing equations for crack layer propagation
Results of analysis on damage distribution of a crack layer, in a model material, supported the self-similarity hypothesis of damage evolution which has been adopted by the crack layer theory. On the basis of measurements of discontinuity density and the double layer potential technique, a solution to the crack damage interaction problem has been developed. Evaluation of the stress intensity factor illustrated the methodology. Analysis of experimental results showed that Arrhenius type constitutive relationship described very well the expansion of the active zone of a crack layer
Translational and extensional energy release rates (the J- and M-integrals) for a crack layer in thermoelasticity
A number of papers have been presented on the evaluation of energy release rate for thermoelasticity and corresponding J integral. Two main approaches were developed to treat energy release rate in elasticity. The first is based on direct calculation of the potential energy rate with respect to crack length. The second makes use of Lagrangian formalism. The translational and expansional energy release rates in thermoelasticity are studied by employing the formalism of irreversible thermodynamics and the Crack Layer Approach
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