25,203 research outputs found
Initial Observations of Sunspot Oscillations Excited by Solar Flare
Observations of a large solar flare of December 13, 2006, using Solar Optical
Telescope (SOT) on Hinode spacecraft revealed high-frequency oscillations
excited by the flare in the sunspot chromosphere. These oscillations are
observed in the region of strong magnetic field of the sunspot umbra, and may
provide a new diagnostic tool for probing the structure of sunspots and
understanding physical processes in solar flares.Comment: 10 pages, 6 figures, ApJL in pres
Off-diagonal magnetoimpedance in field-annealed Co-based amorphous ribbons
The off-diagonal magnetoimpedance in field-annealed CoFeSiB amorphous ribbons
was measured in the low-frequency range using a pick-up coil wound around the
sample. The asymmetric two-peak behavior of the field dependence of the
off-diagonal impedance was observed. The asymmetry is attributed to the
formation of a hard magnetic crystalline phase at the ribbon surface. The
experimental results are interpreted in terms of the surface impedance tensor.
It is assumed that the ribbon consists of an inner amorphous region and surface
crystalline layers. The coupling between the crystalline and amorphous phases
is described through an effective bias field. A qualitative agreement between
the calculated dependences and experimental data is demonstrated. The results
obtained may be useful for development of weak magnetic-field sensors.Comment: 19 pages, 6 figure
Nano granular metallic Fe - oxygen deficient TiO composite films: A room temperature, highly carrier polarized magnetic semiconductor
Nano granular metallic iron (Fe) and titanium dioxide (TiO) were
co-deposited on (100) lanthanum aluminate (LaAlO) substrates in a low
oxygen chamber pressure using a pulsed laser ablation deposition (PLD)
technique. The co-deposition of Fe and TiO resulted in 10 nm
metallic Fe spherical grains suspended within a TiO matrix. The
films show ferromagnetic behavior with a saturation magnetization of 3100 Gauss
at room temperature. Our estimate of the saturation magnetization based on the
size and distribution of the Fe spheres agreed well with the measured value.
The film composite structure was characterized as p-type magnetic semiconductor
at 300 K with a carrier density of the order of . The
hole carriers were excited at the interface between the nano granular Fe and
TiO matrix similar to holes excited in the metal/n-type
semiconductor interface commonly observed in Metal-Oxide-Semiconductor (MOS)
devices. From the large anomalous Hall effect directly observed in these films
it follows that the holes at the interface were strongly spin polarized.
Structure and magneto transport properties suggested that these PLD films have
potential nano spintronics applications.Comment: 6 pages in Latex including 8 figure
Giant Flexoelectric Effect in Ferroelectric Epitaxial Thin Films
We report on nanoscale strain gradients in ferroelectric HoMnO3 epitaxial
thin films, resulting in a giant flexoelectric effect. Using grazing-incidence
in-plane X-ray diffraction, we measured strain gradients in the films, which
were 6 or 7 orders of magnitude larger than typical values reported for bulk
oxides. The combination of transmission electron microscopy, electrical
measurements, and electrostatic calculations showed that flexoelectricity
provides a means of tuning the physical properties of ferroelectric epitaxial
thin films, such as domain configurations and hysteresis curves.Comment: Accepted by Phys. Rev. Let
Electronic Transport in the Oxygen Deficient Ferromagnetic Semiconducting TiO
TiO films were deposited on (100) Lanthanum aluminates
LaAlO substrates at a very low oxygen chamber pressure
mtorr employing a pulsed laser ablation deposition technique. In previous work,
it was established that the oxygen deficiency in these films induced
ferromagnetism. In this work it is demonstrated that this same oxygen
deficiency also gives rise to semiconductor titanium ion impurity donor energy
levels. Transport resistivity measurements in thin films of TiO
are presented as a function of temperature and magnetic field. Magneto- and
Hall- resistivity is explained in terms of electronic excitations from the
titanium ion donor levels into the conduction band.Comment: RevTeX4, Four pages, Four Figures in ^.eps forma
Anomalous kinetics of attractive reactions
We investigate the kinetics of reaction with the local attractive
interaction between opposite species in one spatial dimension. The attractive
interaction leads to isotropic diffusions inside segregated single species
domains, and accelerates the reactions of opposite species at the domain
boundaries. At equal initial densities of and , we analytically and
numerically show that the density of particles (), the size of domains
(), the distance between the closest neighbor of same species
(), and the distance between adjacent opposite species ()
scale in time as , , and respectively. These dynamical exponents form a new
universality class distinguished from the class of uniformly driven systems of
hard-core particles.Comment: 4 pages, 4 figure
Magnetoelectric Effects on Composite Nano Granular Films
Employing a new experimental technique to measure magnetoelectric response
functions, we have measured the magnetoelectric effect in composite films of
nano granular metallic iron in anatase titanium dioxide at temperatures below
50 K. A magnetoelectric resistance is defined as the ratio of a transverse
voltage to bias current as a function of the magnetic field. In contrast to the
anomalous Hall resistance measured above 50 K, the magnetoelectic resistance
below 50 K is significantly larger and exhibits an even symmetry with respect
to magnetic field reversal . The measurement technique required
attached electrodes in the plane of the film composite in order to measure
voltage as a function of bias current and external magnetic field. To our
knowledge, the composite films are unique in terms of showing magnetoelectric
effects at low temperatures, 50 K, and anomalous Hall effects at high
temperatures, 50 K.Comment: ReVTeX, 2 figures, 3 page
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