342 research outputs found
The evolution of Bernstein modes in quantum wires with increasing deviation from parabolic confinement
We investigate the evolution of the interaction of the magnetoplasmon
resonance with the harmonics of the cyclotron resonance as the confinement of
an electron gas in a quantum wire increasingly deviates from the parabolic
case. The occurrence of the Bernstein modes is observed in a time-dependent
Hartree model of a two-dimensional electron gas in a single quantum wire.Comment: 9 pages, 4 figures, uses IOP macros, to appear in the Journal of
Physics: Condensed Matte
Current and Spin-Torque in Double Tunnel Barrier Ferromagnet - Superconductor - Ferromagnet Systems
We calculate the current and the spin-torque in small symmetric double tunnel
barrier ferromagnet - superconductor - ferromagnet (F-S-F) systems.
Spin-accumulation on the superconductor governs the transport properties when
the spin-flip relaxation time is longer than the transport dwell time. In the
elastic transport regime, it is demonstrated that the relative change in the
current (spin-torque) for F-S-F systems equals the relative change in the
current (spin-torque) for F-N-F systems upon changing the relative
magnetization direction of the two ferromagnets. This differs from the results
in the inelastic transport regime where spin-accumulation suppresses the
superconducting gap and dramatically changes the magnetoresistance [S.
Takahashi, H. Imamura, and S. Maekawa, Phys. Rev. Lett. 82, 3911 (1999)]. The
experimental relevance of the elastic and inelastic transport regimes,
respectively, as well as the reasons for the change in the transport properties
are discussed.Comment: 7 page
The effects of compressible and incompressible states on the FIR-absorption of quantum wires and dots in a magnetic field
We investigate the effects of compressible and incompressible states on the
FIR-absorption of quantum wires and dots in a homogeneous perpendicular
magnetic field. The electron-electron interaction is treated in the Hartree
approximation at a finite low temperature. The calculated dispersion of the
collective excitations reproduces several experimental results.Comment: To be published by Physica Scripta in the proceedings of the 17NSM. 6
pages in LaTeX + 6 postscript figure
Current-driven skyrmion Depinning in Magnetic Granular Films
We consider current-driven motion of magnetic skyrmions in granular magnetic
films. The study uses micromagnetic modeling and phenomenological analysis
based on the Thiele formalism. Remarkably, disorder enhances the effective
skyrmion Hall effect that depends on the magnitude of the driving force
(current density and non-adiabaticity parameter). The origin is sliding motion
of the skyrmion along the grain boundaries, followed by pinning and depinning
at the grain junctions. A side-jump can occur during this depinning process. In
addition, the critical current that triggers the skyrmion motion depends on the
relative size of the crystallites with respect to the skyrmion size. Finally,
when the skyrmion trajectory is confined along an edge by the non-adiabatic
Magnus force, the critical current density can be significantly reduced. Our
results imply that narrow nanowires have higher skyrmion mobilities.Comment: 8 pages, 7 figure
Many-body theory of spin-current driven instabilities in magnetic insulators
We consider a magnetic insulator in contact with a normal metal. We derive a
self-consistent Keldysh effective action for the magnon gas that contains the
effects of magnon-magnon interactions and contact with the metal to lowest
order. Self-consistent expressions for the dispersion relation, temperature and
chemical potential for magnons are derived. Based on this effective action, we
study instabilities of the magnon gas that arise due to spin-current flowing
across the interface between the normal metal and the magnetic insulator. We
find that the stability phase diagram is modified by an interference between
magnon-magnon interactions and interfacial magnon-electron coupling. These
effects persist at low temperatures and for thin magnetic insulators.Comment: 10 pages and 5 figure
Magnetoelectronic Spin Echo
We predict a spin echo in electron transport through layered
ferromagnetic-normal-ferromagnetic metal structures: whereas a spin current
polarized perpendicular to the magnetization direction decays when traversing a
single homogeneous ferromagnet on the scale of the ferromagnetic spin-coherence
length, it reappears by adding a second identical but antiparallel ferromagnet.
This re-entrant transverse spin current resembles the spin-echo effect in the
magnetization of nuclei under pulsed excitations. We propose an experimental
setup to measure the magnetoelectronic spin echo.Comment: 4 pages, 2 figure
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