47 research outputs found
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Probing magnetic properties at the nanoscale: in-situ Hall measurements in a TEM
We report on advanced in-situ magneto-transport measurements in a transmission electron microscope. The approach allows for concurrent magnetic imaging and high resolution structural and chemical characterization of the same sample. Proof-of-principle in-situ Hall measurements on presumably undemanding nickel thin films supported by micromagnetic simulations reveal that in samples with non-trivial structures and/or compositions, detailed knowledge of the latter is indispensable for a thorough understanding and reliable interpretation of the magneto-transport data. The proposed in-situ approach is thus expected to contribute to a better understanding of the Hall signatures in more complex magnetic textures
Anomalous Nernst effect in perpendicularly magnetised {\tau}-MnAl thin films
-MnAl is interesting for spintronic applications as a ferromagnet with
perpendicular magnetic anisotropy due to its high uniaxial magnetocrystalline
anisotropy. Here we report on the anomalous Nernst effect of sputter deposited
-MnAl thin films. We demonstrate a robust anomalous Nernst effect at
temperatures of 200 K and 300 K with a hysteresis similar to the anomalous Hall
effect and the magnetisation of the material. The anomalous Nernst coefficient
of (0.60.24) V/K at 300 K is comparable to other perpendicular
magnetic anisotropy thin films. Therefore -MnAl is a promising candidate
for spin-caloritronic research
Generalized Test Tables: A Powerful and Intuitive Specification Language for Reactive Systems
Phase Referencing in Optical Interferometry
One of the aims of next generation optical interferometric instrumentation is
to be able to make use of information contained in the visibility phase to
construct high dynamic range images. Radio and optical interferometry are at
the two extremes of phase corruption by the atmosphere. While in radio it is
possible to obtain calibrated phases for the science objects, in the optical
this is currently not possible. Instead, optical interferometry has relied on
closure phase techniques to produce images. Such techniques allow only to
achieve modest dynamic ranges. However, with high contrast objects, for faint
targets or when structure detail is needed, phase referencing techniques as
used in radio interferometry, should theoretically achieve higher dynamic
ranges for the same number of telescopes. Our approach is not to provide
evidence either for or against the hypothesis that phase referenced imaging
gives better dynamic range than closure phase imaging. Instead we wish to
explore the potential of this technique for future optical interferometry and
also because image reconstruction in the optical using phase referencing
techniques has only been performed with limited success. We have generated
simulated, noisy, complex visibility data, analogous to the signal produced in
radio interferometers, using the VLTI as a template. We proceeded with image
reconstruction using the radio image reconstruction algorithms contained in
AIPS IMAGR (CLEAN algorithm). Our results show that image reconstruction is
successful in most of our science cases, yielding images with a 4
milliarcsecond resolution in K band. (abridged)Comment: 11 pages, 36 figure
Science with a lunar low-frequency array: from the dark ages of the Universe to nearby exoplanets
Low-frequency radio astronomy is limited by severe ionospheric distortions
below 50 MHz and complete reflection of radio waves below 10-30 MHz. Shielding
of man-made interference from long-range radio broadcasts, strong natural radio
emission from the Earth's aurora, and the need for setting up a large
distributed antenna array make the lunar far side a supreme location for a
low-frequency radio array. A number of new scientific drivers for such an
array, such as the study of the dark ages and epoch of reionization,
exoplanets, and ultra-high energy cosmic rays, have emerged and need to be
studied in greater detail. Here we review the scientific potential and
requirements of these and other new scientific drivers and discuss the
constraints for various lunar surface arrays. In particular we describe
observability constraints imposed by the interstellar and interplanetary
medium, calculate the achievable resolution, sensitivity, and confusion limit
of a dipole array using general scaling laws, and apply them to various
scientific questions. Whichever science is deemed most important, pathfinder
arrays are needed to test the feasibility of these experiments in the not too
distant future. Lunar low-frequency arrays are thus a timely option to
consider, offering the potential for significant new insights into a wide range
of today's crucial scientific topics. This would open up one of the last
unexplored frequency domains in the electromagnetic spectrum.Comment: 36 pages, many figures, accepted for publication by New Astronomy
Review
Phase Closure Image Reconstruction for Future VLTI Instrumentation
Classically, optical and near-infrared interferometry have relied on closure
phase techniques to produce images. Such techniques allow us to achieve modest
dynamic ranges. In order to test the feasibility of next generation optical
interferometers in the context of the VLTI-spectro-imager (VSI), we have
embarked on a study of image reconstruction and analysis. Our main aim was to
test the influence of the number of telescopes, observing nights and
distribution of the visibility points on the quality of the reconstructed
images. Our results show that observations using six Auxiliary Telescopes (ATs)
during one complete night yield the best results in general and is critical in
most science cases; the number of telescopes is the determining factor in the
image reconstruction outcome. In terms of imaging capabilities, an optical, six
telescope VLTI-type configuration and ~200 meter baseline will achieve 4 mas
spatial resolution, which is comparable to ALMA and almost 50 times better than
JWST will achieve at 2.2 microns. Our results show that such an instrument will
be capable of imaging, with unprecedented detail, a plethora of sources,
ranging from complex stellar surfaces to microlensing events.Comment: 11 pages, 26 figure
QUAREP-LiMi:A community-driven initiative to establish guidelines for quality assessment and reproducibility for instruments and images in light microscopy
Probing magnetic properties at the nanoscale: in-situ Hall measurements in a TEM
Abstract We report on advanced in-situ magneto-transport measurements in a transmission electron microscope. The approach allows for concurrent magnetic imaging and high resolution structural and chemical characterization of the same sample. Proof-of-principle in-situ Hall measurements on presumably undemanding nickel thin films supported by micromagnetic simulations reveal that in samples with non-trivial structures and/or compositions, detailed knowledge of the latter is indispensable for a thorough understanding and reliable interpretation of the magneto-transport data. The proposed in-situ approach is thus expected to contribute to a better understanding of the Hall signatures in more complex magnetic textures