1,014 research outputs found
Orbital Selective Magnetism in the Spin-Ladder Iron Selenides BaKFeSe
Here we show that the 2.80(8) {\mu}B/Fe block antiferromagnetic order of
BaFe2Se3 transforms into stripe antiferromagnetic order in KFe2Se3 with a
decrease in moment to 2.1(1) {\mu}B/Fe. This reduction is larger than expected
from the change in electron count from Ba to K, and occurs with
the loss of the displacements of Fe atoms from ideal positions in the ladders,
as found by neutron pair distribution function analysis. Intermediate
compositions remain insulating, and magnetic susceptibility measurements show a
suppression of magnetic order and probable formation of a spin-glass. Together,
these results imply an orbital-dependent selection of magnetic versus bonded
behavior, driven by relative bandwidths and fillings.Comment: Final versio
Site Occupancy and Lattice Parameters in Sigma-Phase Co-Cr alloys
Neutron diffraction technique was used to study distribution of Co and Cr
atoms over different lattice sites as well as lattice paramaters in sigma-phase
Co100-xCrx compounds with x = 57.0, 62.7 and 65.8. From the diffractograms
recorded in the temperature range of 4.2 - 300 K it was found that all five
sites A, B, C, D and E are populated by both kinds of atoms. Sites A and D are
predominantly occupied by Co atoms while sites B, C and E by Cr atoms. The unit
cell parameters a and c, hence the unit cell volume, increase with x, the
increase being characteristic of the lattice paramater and temperature. Both a
and c show a non-linear increase with temperature.Comment: 5 figure
Reissner-Nordstrom Expansion
We propose a classical mechanism for the cosmic expansion during the
radiation-dominated era. This mechanism assumes that the Universe is a
two-component gas. The first component is a gas of ultra-relativistic "normal"
particles described by an equation of state of an ideal quantum gas of massless
particles. The second component consist of "unusual" charged particles (namely,
either with ultra-high charge or with ultra-high mass) that provide the
important mechanism of expansion due to their interaction with the "normal"
component of the gas. This interaction is described by the
Reissner--Nordstr\"om metric purely geometrically -- the ``unusual'' particles
are modeled as zero-dimensional naked singularities inside spheres of
gravitational repulsion. The radius of a repulsive sphere is inversely
proportional to the energy of an incoming particle or the temperature. The
expansion mechanism is based on the inflating of the "unusual" particles (of
charge ) with the drop of the temperature -- this drives apart all neutral
particles and particles of specific charge such that . The Reissner--Nordstr\"om expansion naturally ends at recombination. We
discuss the range of model parameters within which the proposed expansion
mechanism is consistent with the restrictions regarding quantum effects.Comment: 9 pages, LaTe
Size distribution of FeNiB nanoparticles
Two samples of amorphous nanoparticles FeNiB, one of them with SiO2 sheath around the core and one without, were investigated by transmission electron microscopy and magnetic measurements. The coating gives mean particle diameters of 4.3 nm compared to 7.2 nm for the uncoated particles. Magnetic measurements prove superparamagnetic behaviour above 160 K (350 K) for the coated (uncoated) sample. With use of effective anisotropy constant Keff – determined from hysteresis loops – size distributions are determined both from ZFC curves, as well as from relaxation measurements. Both are in good agreement and are very similar for both samples. Comparison with the size distribution determined from TEM pictures shows that magnetic clusters consist of only few physical particles
Criteria for the successful completion of medical dissertations – A multicenter study
Objective: In order to acquire the academic title “doctor” in Germany, it is essential to complete a dissertation. A high number of publications at German universities are based on medical dissertations. The reasons why some dissertations are successfully accomplished and why some are not completed – despite far-reaching consequences – have been barely investigated to date
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