159 research outputs found
Direct Observation of Large Amplitude Spin Excitations Localized in a Spin-Transfer Nanocontact
We report the direct observation of large amplitude spin-excitations
localized in a spin-transfer nanocontact using scanning transmission x-ray
microscopy. Experiments were conducted using a nanocontact to an ultrathin
ferromagnetic multilayer with perpendicular magnetic anisotropy. Element
resolved x-ray magnetic circular dichroism images show an abrupt onset of spin
excitations at a threshold current that are localized beneath the nanocontact,
with average spin precession cone angles of 25{\deg} at the contact center. The
results strongly suggest that we have observed a localized magnetic soliton.Comment: 5 pages, 3 figure
Magneto-optical imaging of magnetic deflagration in Mn12-Acetate
For the first time, the morphology and dynamics of spin avalanches in
Mn12-Acetate crystals using magneto-optical imaging has been explored. We
observe an inhomogeneous relaxation of the magnetization, the spins reversing
first at one edge of the crystal and a few milliseconds later at the other end.
Our data fit well with the theory of magnetic deflagration, demonstrating that
very slow deflagration rates can be obtained, which makes new types of
experiments possible.Comment: 5 two-column pages, 3 figures, EPL styl
A copula-based method for synthetic microarray data generation
In this work, we propose a copula-based method to generate synthetic
gene expression data that account for marginal and joint probability distributions
features captured from real data. Our method allows us to implant significant
genes in the synthetic dataset in a controlled manner, giving the possibility of
testing new detection algorithms under more realistic environments
Semiclassical measures and the Schroedinger flow on Riemannian manifolds
In this article we study limits of Wigner distributions (the so-called
semiclassical measures) corresponding to sequences of solutions to the
semiclassical Schroedinger equation at times scales tending to
infinity as the semiclassical parameter tends to zero (when this is equivalent to consider solutions to the non-semiclassical
Schreodinger equation). Some general results are presented, among which a weak
version of Egorov's theorem that holds in this setting. A complete
characterization is given for the Euclidean space and Zoll manifolds (that is,
manifolds with periodic geodesic flow) via averaging formulae relating the
semiclassical measures corresponding to the evolution to those of the initial
states. The case of the flat torus is also addressed; it is shown that
non-classical behavior may occur when energy concentrates on resonant
frequencies. Moreover, we present an example showing that the semiclassical
measures associated to a sequence of states no longer determines those of their
evolutions. Finally, some results concerning the equation with a potential are
presented.Comment: 18 pages; Theorems 1,2 extendend to deal with arbitrary time-scales;
references adde
Phonon-Induced Quantum Magnetic Deflagration in Mn12
A comprehensive set of experiments on the effect of high-frequency surface
acoustic waves, SAWs, in the spin relaxation in Mn12-acetate is presented. We
have studied the quantum magnetic deflagration induced by SAWs under various
experimental conditions extending the data shown in a very recent paper [A.
Hernandez-Minguez et. al., Phys. Rev. Lett. 95, 217205 (2005)]. We have focused
our study on the dependence of both the ignition time and the propagation speed
of the magnetic avalanches on the frequency, amplitude, and duration of the SAW
pulses in experiments performed under different temperatures and external
magnetic fields.Comment: 7 pages, 9 figure
- …