1,882 research outputs found
Reversal and Termination of Current-Induced Domain Wall Motion via Magnonic Spin-Transfer Torque
We investigate the domain wall dynamics of a ferromagnetic wire under the
combined influence of a spin-polarized current and magnonic spin-transfer
torque generated by an external field, taking also into account Rashba
spin-orbit coupling interactions. It is demonstrated that current-induced
motion of the domain wall may be completely reversed in an oscillatory fashion
by applying a magnonic spin-transfer torque as long as the spin-wave velocity
is sufficiently high. Moreover, we show that the motion of the domain wall may
be fully terminated by means of the generation of spin-waves, suggesting the
possibility to pin the domain-walls to predetermined locations. We also discuss
how strong spin-orbit interactions modify these results.Comment: Accepted for publication in Phys. Rev.
Monte Carlo Study of the Square-Lattice Annealed Ising Model on Percolating Clusters
Simulations of an Ising q-state Pods model which is equivalent to the Ising model on annealed percolation clusters are used to determine the phase diagram of the model in two dimensions. Three topologically different phase diagrams are obtained: (i) for q=2, there are two critical Ising lines meeting at T=0 at the four-state Potts critical point; (ii) for 24, the Ising:critical line intersects a Line of first-order transitions at a critical end point
Monte Carlo Study of the Square-Lattice Annealed Ising Model on Percolating Clusters
Simulations of an Ising q-state Pods model which is equivalent to the Ising model on annealed percolation clusters are used to determine the phase diagram of the model in two dimensions. Three topologically different phase diagrams are obtained: (i) for q=2, there are two critical Ising lines meeting at T=0 at the four-state Potts critical point; (ii) for 24, the Ising:critical line intersects a Line of first-order transitions at a critical end point
Phase Diagram of the Ising Model on Percolation Clusters
The annealed Ising magnet on percolation clusters is studied by means of a mapping into a Potts-Ising model and with the Migdal-Kadanoff renormalization-group method. The phase diagram is determined in the three-dimensional parameter space of the Ising coupling K, the bond-occupation probability p, and the fugacity q, which controls the number of clusters. Three phases are identified: percolating ferromagnetic, percolating paramagnetic, and nonpercolating paramagnetic. For large q the phase diagram includes a multicritical point at the intersection of the Ising critical line and the percolation critical line. In the case of random bond percolation (q = 1) the Ising critical line is: p(1 - e-2K) = 1 - exp(- 2L(C)), where Lc is the pure-Ising-model critical coupling
On General Solutions of Einstein Equations
We show how the Einstein equations with cosmological constant (and/or various
types of matter field sources) can be integrated in a very general form
following the anholonomic deformation method for constructing exact solutions
in four and five dimensional gravity (S. Vacaru, IJGMMP 4 (2007) 1285). In this
letter, we prove that such a geometric method can be used for constructing
general non-Killing solutions. The key idea is to introduce an auxiliary linear
connection which is also metric compatible and completely defined by the metric
structure but contains some torsion terms induced nonholonomically by generic
off-diagonal coefficients of metric. There are some classes of nonholonomic
frames with respect to which the Einstein equations (for such an auxiliary
connection) split into an integrable system of partial differential equations.
We have to impose additional constraints on generating and integration
functions in order to transform the auxiliary connection into the Levi-Civita
one. This way, we extract general exact solutions (parametrized by generic
off-diagonal metrics and depending on all coordinates) in Einstein gravity and
five dimensional extensions.Comment: 15 pages, latex2e, submitted to arXiv.org on September 22, 2009,
equivalent to arXiv: 0909.3949v1 [gr-qc]; an extended/modified variant
published in IJTP 49 (2010) 884-913, equivalent to arXiv: 0909.3949v4 [gr-qc
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