493 research outputs found
Electromagnons in the multiferroic state of perovskite manganites with symmetric-exchange striction
We have investigated electrically-active magnetic excitations
(electromagnons) in perovskite manganites with the -type (up-up-down-down)
spin structure by terahertz spectroscopy. EuYMnO (0.11) and YLuMnO (01) without magnetic -moments,
which host collinear sinusoidal, -type, cycloidal, and -type spin orders,
are used to examine the systematics of possible electromagnons. Three-peak
structures (23, 35, 45 cm) of magnetic origin show up in the -type
phase with little composition () dependence of frequencies, making a
contrast with the electromagnons observed in the cycloidal-spin ()
phases. One of these electromagnon is ascribed to the zone-edge magnon mode
based on the calculated magnon dispersions.Comment: 5 pages, 4 figure
Electromagnons in the multiferroic state of perovskite manganites with symmetric-exchange striction
We have investigated electrically-active magnetic excitations
(electromagnons) in perovskite manganites with the -type (up-up-down-down)
spin structure by terahertz spectroscopy. EuYMnO (0.11) and YLuMnO (01) without magnetic -moments,
which host collinear sinusoidal, -type, cycloidal, and -type spin orders,
are used to examine the systematics of possible electromagnons. Three-peak
structures (23, 35, 45 cm) of magnetic origin show up in the -type
phase with little composition () dependence of frequencies, making a
contrast with the electromagnons observed in the cycloidal-spin ()
phases. One of these electromagnon is ascribed to the zone-edge magnon mode
based on the calculated magnon dispersions.Comment: 5 pages, 4 figure
Modelling of platelet aggregation in aneurysm
Thrombi are often found in aneurysms and are considered to play an important role in rupture. It is crucial to scrutinise any correlation between the probability of rupture and the extent to which thrombi are generated in the aneurysm. Numerical techniques such as computational fluid dynamics (CFD) are promising tools in the biomedical field. However, there are, at present, no models that allow us to evaluate thrombus generation. The authors aim at the proposal of such a model. In the present study, the process of platelet aggregation is considered. In blood flow near the entry to an aneurysm, red blood cells are haemolysed due to high shear stress or high pressure. The ensuing release of adenosine diphosphate (ADP) induces the aggregation. Making reference to actual aggregation curves of human plasma for various ADP concentrations, the authors have modelled the rate at which the density of aggregated platelets continues to increase in the aggregation process. A combination of CFD and the present model enables us to obtain the distribution of platelets clotting in an aneurysm
Optical Hall Effect in the Integer Quantum Hall Regime
Optical Hall conductivity is measured from the Faraday
rotation for a GaAs/AlGaAs heterojunction quantum Hall system in the terahertz
frequency regime. The Faraday rotation angle ( fine structure constant
mrad) is found to significantly deviate from the Drude-like behavior to
exhibit a plateau-like structure around the Landau-level filling . The
result, which fits with the behavior expected from the carrier localization
effect in the ac regime, indicates that the plateau structure, although not
quantized, still exists in the terahertz regime.Comment: 4 pages, 4 figure
Electrically driven spin excitation in a ferroelectric magnet DyMnO_3
Temperature (5--250 K) and magnetic field (0--70 kOe) variations of the
low-energy (1--10 meV) electrodynamics of spin excitations have been
investigated for a complete set of light-polarization configurations for a
ferroelectric magnet DyMnO by using terahertz time-domain spectroscopy. We
identify the pronounced absorption continuum (1--8 meV) with a peak feature
around 2 meV, which is electric-dipole active only for the light -vector
along the a-axis. This absorption band grows in intensity with lowering
temperature from the spin-collinear paraelectric phase above the ferroelectric
transition, but is independent of the orientation of spiral spin plane ( or
), as shown on the original (ferroelectric polarization)
phase as well as the magnetic field induced phase. The possible origin of this electric-dipole active band is argued in
terms of the large fluctuations of spins and spin-current.Comment: New version, 11 pages including colored 8 figure
Observation of the spin-charge thermal isolation of ferromagnetic Ga_{0.94}Mn_{0.06}As by time-resolved magneto-optical measurement
The dynamics of magnetization under femtosecond optical excitation is studied
in a ferromagnetic semiconductor Ga_{0.94}Mn_{0.06}As with a time-resolved
magneto-optical Kerr effect measurement with two color probe beams. The
transient reflectivity change indicates the rapid rise of the carrier
temperature and relaxation to a quasi-thermal equilibrium within 1 ps, while a
very slow rise of the spin temperature of the order of 500ps is observed. This
anomalous behavior originates from the thermal isolation between the charge and
spin systems due to the spin polarization of carriers (holes) contributing to
ferromagnetism. This constitutes experimental proof of the half-metallic nature
of ferromagnetic Ga_{0.94}Mn_{0.06}As arising from double exchange type
mechanism originates from the d-band character of holes
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