883 research outputs found
Current-Induced Magnetization Reversal in High Magnetic Fields in Co/Cu/Co Nanopillars
Current-induced magnetization dynamics in Co/Cu/Co trilayer nanopillars
(~100nm in diameter) has been studied experimentally for large applied fields
perpendicular to the layers. An abrupt and hysteretic increase in dynamic
resistance is observed at high current densities for one polarity of the
current, comparable to the giant magnetoresistance effect observed at low
fields. A micromagnetic model, that includes a spin-transfer torque, suggests
that the current induces a complete reversal of the thin Co layer to alignment
antiparallel to the applied field-that is, to a state of maximum magnetic
energy.Comment: 11 pages, 3 figures, (submitted to Phys. Rev. Lett.), added missing
figure caption of fig. 3, updated to published versio
Optical far-infrared properties of graphene monolayer and multilayers
We analyze the features of the graphene mono- and multilayer reflectance in
the far-infrared region as a function of frequency, temperature, and carrier
density taking the intraband conductance and the interband electron absorbtion
into account. The dispersion of plasmon mode of the multilayers is calculated
using Maxwell's equations with the influence of retardation included. At low
temperatures and high electron densities, the reflectance of multilayers as a
function of frequency has the sharp downfall and the subsequent deep well due
to the threshold of electron interband absorbtion.Comment: 9 pages, 4 figure
Current-induced spin-wave excitations in a single ferromagnetic layer
A new current induced spin-torque transfer effect has been observed in a
single ferromagnetic layer without resorting to multilayers. At a specific
current density of one polarity injected from a point contact, abrupt
resistance changes due to current-induced spin wave excitations have been
observed. The critical current at the onset of spin-wave excitations depends
linearly on the external field applied perpendicular to the layer. The observed
effect is due to current-driven heterogeneity in an otherwise uniform
ferromagnetic layer.Comment: 12 pages, 4 figure
Effect of Antiferromagnetic Interlayer Coupling on Current-Assisted Magnetization Switching
We compare magnetization switching in Co/Cu/Co nanopillars with uncoupled and
dipole-field coupled Co layers. In uncoupled nanopillars, current-driven
switching is hysteretic at low magnetic field H and changes to reversible,
characterized by telegraph noise, at high H. We show that dipolar coupling both
affects the switching current and causes the switching to become reversible at
small H. The coupling thus changes the switching to reversible, hysteretic, and
then reversible again as H increases. We describe our results in terms of
current-assisted thermal activation.Comment: 3 pages, 3 figure
Dynamics of Domain Wall in a Biaxial Ferromagnet With Spin-torque
The dynamics of the domain wall (DW) in a biaxial ferromagnet interacting
with a spin-polarized current are described by sine-gordon (SG) equation
coupled with Gilbert damping term in this paper. Within our frame-work of this
model, we obtain a threshold of the current in the motion of a single DW with
the perturbation theory on kink soliton solution to the corresponding
ferromagnetic system, and the threshold is shown to be dependent on the Gilbert
damping term. Also, the motion properties of the DW are discussed for the zero-
and nonzero-damping cases, which shows that our theory to describe the dynamics
of the DW are self-consistent.Comment: 7pages, 3figure
Temperature- and Bias-dependence of magnetoresistance in doped manganite thin film trilayer junctions
Thin film trilayer junction of LaSrMnO - SrTiO -
LaSrMnO shows a factor of 9.7 change in resistance, in a
magnetic field around 100 Oe at 14K. The junction magnetoresistance is bias and
temperature dependent. The energy scales associated with bias and temperature
dependence are an order of magnitude apart. The same set of energies also
determine the bias and temperature dependence of the differential conductance
of the junction. We discuss these results in terms of metallic cluster
inclusions at the junction-barrier interface.Comment: 3 pages, 4 figure
Spin-torque switching: Fokker-Planck rate calculation
We describe a new approach to understanding and calculating magnetization
switching rates and noise in the recently observed phenomenon of "spin-torque
switching". In this phenomenon, which has possible applications to information
storage, a large current passing from a pinned ferromagnetic (FM) layer to a
free FM layer switches the free layer. Our main result is that the spin-torque
effect increases the Arrhenius factor in the switching rate, not
by lowering the barrier , but by raising the effective spin temperature .
To calculate this effect quantitatively, we extend Kramers' 1940 treatment of
reaction rates, deriving and solving a Fokker-Planck equation for the energy
distribution including a current-induced spin torque of the Slonczewski type.
This method can be used to calculate slow switching rates without long-time
simulations; in this Letter we calculate rates for telegraph noise that are in
good qualitative agreement with recent experiments. The method also allows the
calculation of current-induced magnetic noise in CPP (current perpendicular to
plane) spin valve read heads.Comment: 11 pages, 8 figures, 1 appendix Original version in Nature format,
replaced by Phys. Rev. Letters format. No substantive change
Rotating vortex dipoles in ferromagnets
Vortex-antivortex pairs are localized excitations and have been found to be
spontaneously created in magnetic elements. In the case that the vortex and the
antivortex have opposite polarities the pair has a nonzero topological charge,
and it behaves as a rotating vortex dipole. We find theoretically, and confirm
numerically, the form of the energy as a function of the angular momentum of
the system and the associated rotation frequencies. We discuss the process of
annihilation of the pair which changes the topological charge of the system by
unity while its energy is monotonically decreasing. Such a change in the
topological charge affects profoundly the dynamics in the magnetic system. We
finally discuss the connection of our results with Bloch Points (BP) and the
implications for BP dynamics.Comment: 6 pages, 2 figure
Thin-Film Trilayer Manganate Junctions
Spin-dependent conductance across a manganate-barrier-manganate junction has
recently been demonstrated. The junction is a LaSrMnO%
-SrTiO-La SrMnO trilayer device supporting
current-perpendicular transport. Large magnetoresistance of up to a factor of
five change was observed in these junctions at 4.2K in a relatively low field
of the order of 100 Oe. Temperature and bias dependent studies revealed a
complex junction interface structure whose materials physics has yet to be
understood.Comment: 20 pages, 14 figures. To appear in Phil. Trans. R. Soc. Lond. A
vol.356 (1998
Current induced transverse spin-wave instability in thin ferromagnets: beyond linear stability analysis
A sufficiently large unpolarized current can cause a spin-wave instability in
thin nanomagnets with asymmetric contacts. The dynamics beyond the instability
is understood in the perturbative regime of small spin-wave amplitudes, as well
as by numerically solving a discretized model. In the absence of an applied
magnetic field, our numerical simulations reveal a hierarchy of instabilities,
leading to chaotic magnetization dynamics for the largest current densities we
consider.Comment: 14 pages, 10 figures; revtex
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