790 research outputs found
Domain-wall resistance in ferromagnetic (Ga,Mn)As
A series of microstructures designed to pin domain-walls (DWs) in (Ga,Mn)As
with perpendicular magnetic anisotropy has been employed to determine extrinsic
and intrinsic contributions to DW resistance. The former is explained
quantitatively as resulting from a polarity change in the Hall electric field
at DW. The latter is one order of magnitude greater than a term brought about
by anisotropic magnetoresistance and is shown to be consistent with
disorder-induced misstracing of the carrier spins subject to spatially varying
magnetization
CoFeB Thickness Dependence of Thermal Stability Factor in CoFeB/MgO Perpendicular Magnetic Tunnel Junctions
Thermal stability factor (delta) of recording layer was studied in
perpendicular anisotropy CoFeB/MgO magnetic tunnel junctions (p-MTJs) with
various CoFeB recording layer thicknesses and junction sizes. In all series of
p-MTJs with different thicknesses, delta is virtually independent of the
junction sizes of 48-81 nm in diameter. The values of delta increase linearly
with increasing the recording layer thickness. The slope of the linear fit is
explained well by a model based on nucleation type magnetization reversal.Comment: 12 pages, 5 figure
Velocity of domain-wall motion induced by electrical current in a ferromagnetic semiconductor (Ga,Mn)As
Current-induced domain-wall motion with velocity spanning over five orders of
magnitude up to 22 m/s has been observed by magneto-optical Kerr effect in
(Ga,Mn)As with perpendicular magnetic anisotropy. The data are employed to
verify theories of spin-transfer by the Slonczewski-like mechanism as well as
by the torque resulting from spin-flip transitions in the domain-wall region.
Evidence for domain-wall creep at low currents is found.Comment: 5 pages, 3 figure
Domain structure in CoFeB thin films with perpendicular magnetic anisotropy
Domain structures in CoFeB-MgO thin films with a perpendicular easy
magnetization axis were observed by magneto-optic Kerr-effect microscopy at
various temperatures. The domain wall surface energy was obtained by analyzing
the spatial period of the stripe domains and fitting established domain models
to the period. In combination with SQUID measurements of magnetization and
anisotropy energy, this leads to an estimate of the exchange stiffness and
domain wall width in these films. These parameters are essential for
determining whether domain walls will form in patterned structures and devices
made of such materials
Magnetoresistance Anomalies in (Ga,Mn)As Epilayers with Perpendicular Magnetic Anisotropy
We report the observation of anomalies in the longitudinal magnetoresistance
of tensile-strained (Ga,Mn)As epilayers with perpendicular magnetic anisotropy.
Magnetoresistance measurements carried out in the planar geometry (magnetic
field parallel to the current density) reveal "spikes" that are antisymmetric
with respect to the direction of the magnetic field. These anomalies always
occur during magnetization reversal, as indicated by a simultaneous change in
sign of the anomalous Hall effect. The data suggest that the antisymmetric
anomalies originate in anomalous Hall effect contributions to the longitudinal
resistance when domain walls are located between the voltage probes. This
interpretation is reinforced by carrying out angular sweeps of ,
revealing an antisymmetric dependence on the helicity of the field sweep.Comment: Submitted to Phys. Rev.
Properties of aerosols and their wet deposition in the arctic spring during ASTAR2004 at Ny-Alesund, Svalbard
During the period of scientific campaign "Arctic Study of Tropospheric Aerosols, Clouds and Radiation 2004" (ASTAR2004), precipitation samples were collected in late spring at Ny-Alesund, Svalbard and their ionic components were analyzed in parallel with the measurement of properties of atmospheric aerosol particles at the same place. Backward trajectory analyses indicated that the air mass above the observatory initially dominated by air masses from the Arctic Ocean, then those from western Siberia and later those from Greenland and the Arctic Ocean. In the measurement period, six precipitation samples were obtained and five of them were analyzed their ionic components by ionchromatography. The concentrations of nss-sulphate in precipitations were between 1.8 and 24.6 ppm from which the scavenging ratio and scavenging coefficients were calculated using the data such as the concentrations of nss-sulphate in aerosol particles, amounts of precipitations, and the heights of precipitations obtained from radar echo data. The scavenging ratio ranged from 1.0&times;10<sup>6</sup> to 17&times;10<sup>6</sup> which are comparable values reported in other areas. A detailed comparison between precipitation events and the number concentration of aerosol particles obtained from optical particle counters suggests that the type of precipitations, i.e. rain or snow, significantly affects the number concentrations of aerosol particles
Nonlinear Conduction by Melting of Stripe-Type Charge Order in Organic Conductors with Triangular Lattices
We theoretically discuss the mechanism for the peculiar nonlinear conduction
in quasi-two-dimensional organic conductors \theta-(BEDT-TTF)2X
[BEDT-TTF=bis(ethylenedithio)tetrathiafulvalene] through the melting of
stripe-type charge order. An extended Peierls-Hubbard model attached to
metallic electrodes is investigated by a nonequilibrium Green's function
technique. A novel current-voltage characteristic appears in a coexistent state
of stripe-type and nonstripe 3-fold charge orders, where the applied bias melts
mainly the stripe-type charge order through the reduction of lattice
distortion, whereas the 3-fold charge order survives. These contrastive
responses of the two different charge orders are consistent with the
experimental observations.Comment: 5 pages, 4 figures, to appear in J. Phys. Soc. Jp
Stripe orders in the extended Hubbard model
We study stripe orders of charge and spin density waves in the extended
Hubbard model with the nearest-neighbor Coulomb repulsion V within the mean
field approximation. We obtain V vs. T(temperature) phase diagram for the
on-site Coulomb interaction U/t=8.0 and the filling n=0.8, here t is a
nearest-neighbor transfer energy. Our result shows that the diagonal stripe
spin density wave state (SDW) is stable for small V, but for large V the most
stable state changes to a charge density wave-antiferromagnetic (CDW-AF) state.
Especially we find at low temperature and for a certain range of value of V, a
vertical stripe CDW-AF state becomes stable.Comment: LaTeX 9 pages, 17 figures, uses jpsj.st
Quantized Adiabatic Charge Transport in a Carbon Nanotube
The coupling of a metallic Carbon nanotube to a surface acoustic wave (SAW)
is proposed as a vehicle to realize quantized adiabatic charge transport in a
Luttinger liquid system. We demonstrate that electron backscattering by a
periodic SAW potential, which results in miniband formation, can be achieved at
energies near the Fermi level. Electron interaction, treated in a Luttinger
liquid framework, is shown to enhance minigaps and thereby improve current
quantization. Quantized SAW induced current, as a function of electron density,
changes sign at half-filling.Comment: 5 pages, 2 figure
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