51,610 research outputs found
Optimization of -Layer Systems for Josephson Junctions from a Microstructure Point of View
-layer systems are frequently used for Josephson junction-based
superconducting devices. Although much work has been devoted to the
optimization of the superconducting properties of these devices, systematic
studies on influence of deposition conditions combined with structural analyses
on the nanoscale are rare up to now. We have focused on the optimization of the
structural properties of -layer systems deposited on Si(111)
substrates with a particular focus on the thickness homogeneity of the
-tunnel barrier. A standard high-vacuum electron-beam deposition system
was used and the effect of substrate pretreatment, different Al-deposition
temperatures and Al-deposition rates was studied. Transmission electron
microscopy was applied to analyze the structural properties of the
-layer systems to determine the thickness homogeneity of the
layer, grain size distribution in the Al layers, Al-grain boundary
types and the morphology of the interface. We show that the
structural properties of the lower Al layer are decisive for the structural
quality of the whole -layer system. Optimum conditions yield an
epitaxial Al(111) layer on a Si(111) substrate with an Al-layer thickness
variation of only 1.6 nm over more than 10 and large lateral grain
sizes up to 1 . Thickness fluctuations of the -tunnel barrier are
minimized on such an Al layer which is essential for the homogeneity of the
tunnel current. Systematic variation of the Al-deposition rate and deposition
temperature allows to develop an understanding of the growth mechanisms
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Situating multimodal learning analytics
The digital age has introduced a host of new challenges and opportunities for the learning sciences community. These challenges and opportunities are particularly abundant in multimodal learning analytics (MMLA), a research methodology that aims to extend work from Educational Data Mining (EDM) and Learning Analytics (LA) to multimodal learning environments by treating multimodal data. Recognizing the short-term opportunities and longterm challenges will help develop proof cases and identify grand challenges that will help propel the field forward. To support the field's growth, we use this paper to describe several ways that MMLA can potentially advance learning sciences research and touch upon key challenges that researchers who utilize MMLA have encountered over the past few years
Structural and magneto-transport characterization of Co_2Cr_xFe_(1-x)Al Heusler alloy films
We investigate the structure and magneto-transport properties of thin films
of the Co_2Cr_xFe_(1-x)Al full-Heusler compound, which is predicted to be a
half-metal by first-principles theoretical calculations. Thin films are
deposited by magnetron sputtering at room temperature on various substrates in
order to tune the growth from polycrystalline on thermally oxidized Si
substrates to highly textured and even epitaxial on MgO(001) substrates,
respectively. Our Heusler films are magnetically very soft and ferromagnetic
with Curie temperatures up to 630 K. The total magnetic moment is reduced
compared to the theoretical bulk value, but still comparable to values reported
for films grown at elevated temperature. Polycrystalline Heusler films combined
with MgO barriers are incorporated into magnetic tunnel junctions and yield 37%
magnetoresistance at room temperature
Influence of point defects on magnetic vortex structures
We employed micro-Hall magnetometry and micromagnetic simulations to
investigate magnetic vortex pinning at single point defects in individual
submicron-sized permalloy disks. Small ferromagnetic particles containing
artificial point defects can be fabricated by using an image reversal electron
beam lithography process. Corresponding micromagnetic calculations, modeling
the defects within the disks as holes, give reasonable agreement between
experimental and simulated pinning and depinning field values
Implications of the isotope effects on the magnetization, magnetic torque and susceptibility
We analyze the magnetization, magnetic torque and susceptibility data of
La2-xSrxCu(16,18)O4 and YBa2(63,65)CuO7-x near Tc in terms of the universal
3D-XY scaling relations. It is shown that the isotope effect on Tc mirrors that
on the anisotropy. Invoking the generic behavior of the anisotropy the doping
dependence of the isotope effects on the critical properties, including Tc,
correlation lengths and magnetic penetration depths are traced back to a change
of the mobile carrier concentration.Comment: 5 pages, 3 figure
Characterization of low loss microstrip resonators as a building block for circuit QED in a 3D waveguide
Here we present the microwave characterization of microstrip resonators made
from aluminum and niobium inside a 3D microwave waveguide. In the low
temperature, low power limit internal quality factors of up to one million were
reached. We found a good agreement to models predicting conductive losses and
losses to two level systems for increasing temperature. The setup presented
here is appealing for testing materials and structures, as it is free of wire
bonds and offers a well controlled microwave environment. In combination with
transmon qubits, these resonators serve as a building block for a novel circuit
QED architecture inside a rectangular waveguide
Thickness dependence of linear and quadratic magneto-optical Kerr effect in ultrathin Fe(001) films
Magneto-optical Kerr effect (MOKE) magnetometry is one of the most widely
employed techniques for the characterization of ferromagnetic thin-film
samples. Some information, such as coercive fields or anisotropy strengths can
be obtained without any knowledge of the optical and magneto-optical (MO)
properties of the material. On the other hand, a quantitative analysis, which
requires a precise knowledge of the material's index of refraction n and the MO
coupling constants K and G is often desirable, for instance for the comparison
of samples, which are different with respect to ferromagnetic layer
thicknesses, substrates, or capping layers. While the values of the parameters
n and the linear MO coupling parameter K reported by different authors usually
vary considerably, the relevant quadratic MO coupling parameters G of Fe are
completely unknown. Here, we report on measurements of the thickness dependence
(0-60nm) of the linear and quadratic MOKE in epitaxial bcc-Fe(001) wedge-type
samples performed at a commonly used laser wavelength of 670nm. By fitting the
thickness dependence we are able to extract a complete set of parameters n, K,
(G11 - G12), and G44 for the quantitative description of the MOKE of
bcc-Fe(001). We find sizable different n, K, and G parameters for films thinner
than about 10nm as compared to thicker films, which is indicative of a
thickness dependence of the electronic properties or of surface contributions
to the MOKE. The effect size of the quadratic MOKE is found to be about a third
of the record values recently reported for Co2FeSi.Comment: 8 pages, 5 figure
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