277 research outputs found
The cleavage surface of the BaFe_(2-x)Co_(x)As_(2) and Fe_(y)Se_(1-x)Te_(x) superconductors: from diversity to simplicity
We elucidate the termination surface of cleaved single crystals of the
BaFe_(2-x)Co_(x)As_(2) and Fe_(y)Se_(1-x)Te_(x) families of the high
temperature iron based superconductors. By combining scanning tunneling
microscopic data with low energy electron diffraction we prove that the
termination layer of the Ba122 systems is a remnant of the Ba layer, which
exhibits a complex diversity of ordered and disordered structures. The observed
surface topographies and their accompanying superstructure reflections in
electron diffraction depend on the cleavage temperature. In stark contrast,
Fe_(y)Se_(1-x)Te_(x) possesses only a single termination structure - that of
the tetragonally ordered Se_(1-x)Te_(x) layer.Comment: 4 pages, 4 figure
Fabrication of magnetic atom chips based on FePt
We describe the design and fabrication of novel all-magnetic atom chips for
use in ultracold atom trapping. The considerations leading to the choice of
nanocrystalline exchange coupled FePt as best material are discussed. Using
stray field calculations, we designed patterns that function as magnetic atom
traps. These patterns were realized by spark erosion of FePt foil and e-beam
lithography of FePt film. A mirror magneto-optical trap (MMOT) was obtained
using the stray field of the foil chip.Comment: 5 pages, 5 figure
X-ray magneto-optics of lanthanide materials: principles and applications
Lanthanide metals are a particular class of magnetic materials in which the
magnetic moments are carried mainly by the localized electrons of the 4f shell.
They are frequently found in technically relevant systems, to achieve, e.g.,
high magnetic anisotropy. Magneto-optical methods in the x-ray range are well
suited to study complex magnetic materials in an element-specific way. In this
work, we report on recent progress on the quantitative determination of
magneto-optical constants of several lanthanides in the soft x-ray region and
we show some examples of applications of magneto-optics to hard-magnetic
interfaces and exchange-coupled layered structures containing lanthanide
elements.Comment: 7 pages, 6 figures, invited contribution to the Symposium "X-ray
magneto-optics" of the Spring Meeting of the German Physical Society held in
Regensburg, Germany, 8-12 March 2004. Revised version, minor change
A high resolution, hard x-ray photoemission investigation of La_(2-2x)Sr_(1+2x)Mn_2O_7 (0.30<x<0.50): on microscopic phase separation and the surface electronic structure of a bilayered CMR manganite
Photoemission data taken with hard x-ray radiation on cleaved single crystals
of the bilayered, colossal magnetoresistant manganite La_(2-2x)Sr_(1+2x)Mn_2O_7
(LSMO) with 0.30<x<0.50 are presented. Making use of the increased
bulk-sensitivity upon hard x-ray excitation it is shown that the core level
footprint of the electronic structure of the LSMO cleavage surface is identical
to that of the bulk. Furthermore, by comparing the core level shift of the
different elements as a function of doping level x, it is shown that
microscopic phase separation is unlikely to occur for this particular manganite
well above the Curie temperature.Comment: 7 pages, 5 figure
The Role of Community in Understanding Involvement in Community Energy Initiatives
Community energy initiatives are set up by volunteers in local communities to promote sustainable energy behaviors and help to facilitate a sustainable energy transition. A key question is what motivates people to be involved in such initiatives. We propose that next to a stronger personal motivation for sustainable energy, people’s perception that their community is motivated to engage in sustainable energy and their involvement in the community (i.e., community identification and interpersonal contact) may affect their initiative involvement. We tested this proposition with a questionnaire study among inhabitants of seven local communities (N = 439). Results suggested that community factors are uniquely related to initiative involvement (willingness to actively participate and attendance of an initiative meeting) next to personal sustainable energy motivations. In particular, stronger community identification and more interpersonal contact with other community members increased the likelihood that people become involved in a community initiative, but the perception of the sustainable energy motivation of one’s community was not uniquely related to initiative involvement. We discuss theoretical and practical implications of these findings
Nanoscale superconducting gap variations, strong coupling signatures and lack of phase separation in optimally doped BaFe1.86Co0.14As2
We present tunneling data from optimally-doped, superconducting
BaFe1.86Co0.14As2 and its parent compound, BaFe2As2. In the superconductor,
clear coherence-like peaks are seen across the whole field of view, and their
analysis reveals nanoscale variations in the superconducting gap value, Delta.
The average magnitude of 2Delta is ~7.4 kBTC, which exceeds the BCS weak
coupling value for either s- or d-wave superconductivity. The characteristic
length scales of the deviations from the average gap value, and of an
anti-correlation discovered between the gap magnitude and the zero bias
conductance, match well with the average separation between the Co dopant ions
in the superconducting FeAs planes. The tunneling spectra themselves possess a
peak-dip-hump lineshape, suggestive of a coupling of the superconducting
electronic system to a well-defined bosonic mode of energy 4.7 kBTC, such as
the spin resonance observed recently in inelastic neutron scattering.Comment: 4 figures, corrected typos, reduced size of image
Magnetization reversal, asymmetry, and role of uncompensated spins in perpendicular exchange coupled systems
This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.Soft x-ray resonant magnetic scattering has been used to investigate the element-selective microscopic magnetization reversal behavior of room temperature perpendicular exchange coupled ferromagnetic∕antiferromagnetic (F∕AF) systems and to study the role of the interfacial coupling strength on it. Different nucleation processes and domain size distributions along the decreasing and increasing branches of the reversal have been found. The size of the magnetic domains during reversal depends on both the F anisotropy and F∕AF coupling strength, decreasing when one of them increases. Evidence of the exchange bias(coercivity enhancement) being induced by pinned (unpinned) uncompensated AF interfacial spins is also shown
Rare earth contributions to the X-ray magnetic circular dichroism at the Co K edge in rare earth-cobalt compounds investigated by multiple-scattering calculations
The X-ray magnetic circular dichroism (XMCD) has been measured at the Co K
edge in Co-hcp and R-Co compounds (R=La, Tb, Dy). The structure of the
experimental XMCD spectra in the near-edge region has been observed to be
highly sensitive to the magnetic environment of the absorbing site.
Calculations of the XMCD have been carried out at the Co K edge in Co metal,
LaCo and TbCo within the multiple-scattering framework including the
spin-orbit coupling. In the three systems, the XMCD spectra in the near-edge
region are well reproduced. The possibility to separate and quantitatively
estimate the local effects from those due to the neighboring atoms in the XMCD
cross section makes possible a more physical understanding of the spectra. The
present results emphasize the major role played by the states of the Tb
ions in the XMCD spectrum at the Co K edge in the TbCo compound.Comment: 34 pages, revtex, 10 eps figures included with epsf, after referee
revie
Pseudogap-less high T superconductivity in BaCoFeAs
The pseudogap state is one of the peculiarities of the cuprate high
temperature superconductors. Here we investigate its presence in
BaCoFeAs, a member of the pnictide family, with temperature
dependent scanning tunneling spectroscopy. We observe that for under, optimally
and overdoped systems the gap in the tunneling spectra always closes at the
bulk T, ruling out the presence of a pseudogap state. For the underdoped
case we observe superconducting gaps over large fields of view, setting a lower
limit of tens of nanometers on the length scale of possible phase separated
regions.Comment: 5 pages, 3 figure
- …