77 research outputs found
Domain walls in helical magnets
The structure of domain walls determines to a large extent the properties of
magnetic materials, in particular their hardness and switching behavior, it
represents an essential ingredient of spintronics. Common domain walls are of
Bloch and Neel types in which the magnetization rotates around a fixed axis,
giving rise to a one-dimensional magnetization profile. Domain walls in helical
magnets, most relevant in multiferroics, were never studied systematically.
Here we show that domain walls in helical magnets are fundamentally different
from Bloch and Neel walls. They are generically characterized by a
two-dimensional pattern formed by a regular lattice of vortex singularities. In
conical phases vortices carry Berry phase flux giving rise to the anomalous
Hall effect. In multiferroics vortices are charged, allowing to manipulate
magnetic domain walls by electric fields. Our theory allows the interpretation
of magnetic textures observed in helical magnetic structures
Phase Diagram for Magnon Condensate in Yttrium Iron Garnet Film
Recently, magnons, which are quasiparticles describing the collective motion
of spins, were found to undergo Bose-Einstein condensation (BEC) at room
temperature in films of Yttrium Iron Garnet (YIG). Unlike other quasiparticle
BEC systems, this system has a spectrum with two degenerate minima, which makes
it possible for the system to have two condensates in momentum space. Recent
Brillouin Light scattering studies for a microwave-pumped YIG film of thickness
d=5 m and field H=1 kOe find a low-contrast interference pattern at the
characteristic wavevector of the magnon energy minimum. In this report, we
show that this modulation pattern can be quantitatively explained as due to
non-symmetric but coherent Bose-Einstein condensation of magnons into the two
energy minima. Our theory predicts a transition from a high-contrast symmetric
phase to a low-contrast non-symmetric phase on varying the and , and a
new type of collective oscillations.Comment: 6 figures. Accepted by Nature Scientific Report
In situ defect annealing of swift heavy ion irradiated CeO2 and ThO2 using synchrotron Xâray diffraction and a hydrothermal diamond anvil cell
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111991/1/S160057671500477X.pd
Scale invariance of a diodelike tunnel junction
We measure the current vs voltage (I-V) characteristics of a diodelike tunnel
junction consisting of a sharp metallic tip placed at a variable distance d
from a planar collector and emitting electrons via electric-field assisted
emission. All curves collapse onto one single graph when I is plotted as a
function of the single scaling variable Vd^{-\lambda}, d being varied from a
few mm to a few nm, i.e., by about six orders of magnitude. We provide an
argument that finds the exponent {\lambda} within the singular behavior
inherent to the electrostatics of a sharp tip. A simulation of the tunneling
barrier for a realistic tip reproduces both the scaling behavior and the small
but significant deviations from scaling observed experimentally.Comment: 6 pages, 6 figures. Accepted for publication in Physical Review
Preparation, characterization and catalytic applications of ZrO2 supported on low cost SBA-15
This work presents some applications of ZrO2 supported over SBA-15 silica as promoter of sulfated zirconia and as support from CuO/CeO 2 catalytic system for preferential oxidation of CO to CO2 in hydrogen rich streams, used as feed for proton exchange membrane fuel cells (PEMFC). Different amounts of ZrO2, from 10 to 30 wt.% were incorporated. These prepared materials were characterized by powder XRD, adsorption-desorption of N2 at 77 K, transmission and scanning electron microscopy (TEM and SEM) and X-rays photoelectron spectroscopy (XPS). The acidity was studied by thermo-programmed desorption of ammonia (NH 3-TPD). These materials were tested, after treatment with H 2SO4, by 2-propanol dehydration and 1-butene isomerization catalytic tests. The samples were found quite good catalyst with strong acid sites, the sample with 20 wt.% of ZrO2 being the better performing sample. Finally this material was successfully used as support for a CuO/CeO2 system, with 6 wt.% of Cu and 20 wt.% of Ce. The resulting catalyst was tested in the preferential oxidation of CO (CO-PROX) attaining conversions close to 100% and high selectivity to CO2
Extended Haldane's model and its simulation with ultracold atoms
Haldane's model is extended to a square lattice related close to the so-called state, in which the on-site energy is staggered and the next-nearest-neighbor hopping is anisotropic. From the phase diagram obtained, two types of phases are found, i.e., the normal insulator with Chern number and the Hall insulator with C = ± 1. We propose a way of simulating this model with cold atoms in an optical lattice. By measuring the atomic density profile, one can detect this phase diagram
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