1,645 research outputs found
Pump-Probe Experiments on the Single-Molecule Magnet Fe8 : Measurement of Excited Level Lifetimes
We present magnetization measurements on the single molecule magnet Fe8 in
the presence of pulsed microwave radiation. A pump-probe technique is used with
two microwave pulses with frequencies of 107 GHz and 118 GHz and pulse lengths
of several nanoseconds to study the spin dynamics via time-resolved
magnetization measurements using a Hall probe magnetometer. We find evidence
for short spin-phonon relaxation times of the order of one microsecond. The
temperature dependence of the spin-phonon relaxation time in our experiments is
in good agreement with previously published theoretical results. We also
established the presence of very short energy diffusion times, that act on a
timescale of about 70 ns.Comment: submitted to Phys. Rev. Lett. (01 March 2007
Self-organized escape of oscillator chains in nonlinear potentials
We present the noise free escape of a chain of linearly interacting units
from a metastable state over a cubic on-site potential barrier. The underlying
dynamics is conservative and purely deterministic. The mutual interplay between
nonlinearity and harmonic interactions causes an initially uniform lattice
state to become unstable, leading to an energy redistribution with strong
localization. As a result a spontaneously emerging localized mode grows into a
critical nucleus. By surpassing this transition state, the nonlinear chain
manages a self-organized, deterministic barrier crossing. Most strikingly,
these noise-free, collective nonlinear escape events proceed generally by far
faster than transitions assisted by thermal noise when the ratio between the
average energy supplied per unit in the chain and the potential barrier energy
assumes small values
Thermal suppression of surface barrier in ultrasmall superconducting structures
In the recent experiment by Cren \textit{et al.} [Phys. Rev. Lett.
\textbf{102}, 127005 (2009)], no hysteresis for vortex penetration and
expulsion from the nano-island of Pb was observed. In the present paper, we
argue that this effect can be associated with the thermoactivated surmounting
of the surface barrier by a vortex. The typical entrance (exit) time is found
analytically from the Fokker-Planck equation, written in the form suitable for
the extreme vortex confinement. We show that this time is several orders of
magnitude smaller than 1 second under the conditions of the experiment
considered. Our results thus demonstrate a possibility for the thermal
suppression of the surface barrier in nanosized low- superconductors. We
also briefly discuss other recent experiments on vortices in related
structures.Comment: 12 pages, 2 figure
Piezomagnetic Quantum Dots
We study the influence of deformations on magnetic ordering in quantum dots
doped with magnetic impurities. The reduction of symmetry and the associated
deformation from circular to elliptical quantum confinement lead to the
formation of piezomagnetic quantum dots. The strength of elliptical deformation
can be controlled by the gate voltage to change the magnitude of magnetization,
at a fixed number of carriers and in the absence of applied magnetic field. We
reveal a reentrant magnetic ordering with the increase of elliptical
deformation and suggest that the piezomagnetic quantum dots can be used as
nanoscale magnetic switches.Comment: 4 pages, 3 figure
Formation of non-state pension system in the Russian Federation on an example of the activities of non-state pension fund "Sberbank"
The article is devoted to a problem, which is important relevant for the Russian Federation.it is studying the factors of formation of non-state system in provision of pensions.
In this article, the authors have described the russian specifics of formation in the system of non-state pension provision in the Russian Federation. As the main methods, the system and structural and analytical analysis are chosen. Data and materials of the non-state pension fund of Sberbank became material of a research.
The main documents regulating formations and functioning of the non-state pension funds are submitted. It is shown that one of the most perspective is activity of the non-state pension fund of Sberbank.
The sources of formation of revenues of the non-state pension fund of Sberbank are described. Both individual and corporate programs of the non-state pension fund of Sberbank are submitted.
The conducted research allows making conclusions that despite the undertaken reforms of provision of pensions by the citizens.peer-reviewe
Magnetization dynamics in the single-molecule magnet Fe8 under pulsed microwave irradiation
We present measurements on the single molecule magnet Fe8 in the presence of
pulsed microwave radiation at 118 GHz. The spin dynamics is studied via time
resolved magnetization experiments using a Hall probe magnetometer. We
investigate the relaxation behavior of magnetization after the microwave pulse.
The analysis of the experimental data is performed in terms of different
contributions to the magnetization after-pulse relaxation. We find that the
phonon bottleneck with a characteristic relaxation time of 10 to 100 ms
strongly affects the magnetization dynamics. In addition, the spatial effect of
spin diffusion is evidenced by using samples of different sizes and different
ways of the sample's irradiation with microwaves.Comment: 14 pages, 12 figure
Complete spin polarization of electrons in semiconductor layers and quantum dots
We demonstrate that non-equilibrium electrons in thin nonmagnetic
semiconductor layers or quantum dots can be fully spin polarized by means of
simultaneous electrical spin injection and extraction. The complete spin
polarization is achieved if the thin layers or quantum dots are placed between
two ferromagnetic metal contacts with moderate spin injection coefficients and
antiparallel magnetizations. The sign of the spin polarization is determined by
the direction of the current. Aplications of this effect in spintronics and
quantum information processing are discussed
Spin-dependent resonant tunneling through semimetallic ErAs quantum wells
Resonant tunneling through semimetallic ErAs quantum wells embedded in GaAs
structures with AlAs barriers was recently found to exhibit an intriguing
behavior in magnetic fields which is explained in terms of tunneling selection
rules and the spin-polarized band structure including spin-orbit coupling.Comment: 4 pages, figures supplied as self-unpacking figures.uu, uses
epsfig.sty to incorporate figures in preprin
Magnetism in Closed-shell Quantum Dots: Emergence of Magnetic Bipolarons
Similar to atoms and nuclei, semiconductor quantum dots exhibit formation of
shells. Predictions of magnetic behavior of the dots are often based on the
shell occupancies. Thus, closed-shell quantum dots are assumed to be inherently
nonmagnetic. Here, we propose a possibility of magnetism in such dots doped
with magnetic impurities. On the example of the system of two interacting
fermions, the simplest embodiment of the closed-shell structure, we demonstrate
the emergence of a novel broken-symmetry ground state that is neither
spin-singlet nor spin-triplet. We propose experimental tests of our predictions
and the magnetic-dot structures to perform them.Comment: 4 pages, 4 figures;
http://link.aps.org/doi/10.1103/PhysRevLett.106.177201; minor change
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