573 research outputs found
Cubic anisotropy in high homogeneity thin (Ga,Mn)As layers
Historically, comprehensive studies of dilute ferromagnetic semiconductors,
e.g., -type (Cd,Mn)Te and (Ga,Mn)As, paved the way for a quantitative
theoretical description of effects associated with spin-orbit interactions in
solids, such as crystalline magnetic anisotropy. In particular, the theory was
successful in explaining {\em uniaxial} magnetic anisotropies associated with
biaxial strain and non-random formation of magnetic dimers in epitaxial
(Ga,Mn)As layers. However, the situation appears much less settled in the case
of the {\em cubic} term: the theory predicts switchings of the easy axis
between in-plane and directions as a
function of the hole concentration, whereas only the
orientation has been found experimentally. Here, we report on the observation
of such switchings by magnetization and ferromagnetic resonance studies on a
series of high-crystalline quality (Ga,Mn)As films. We describe our findings by
the mean-field - Zener model augmented with three new ingredients. The
first one is a scattering broadening of the hole density of states, which
reduces significantly the amplitude of the alternating carrier-induced
contribution. This opens the way for the two other ingredients, namely the
so-far disregarded single-ion magnetic anisotropy and disorder-driven
non-uniformities of the carrier density, both favoring the
direction of the apparent easy axis. However, according to our results, when
the disorder gets reduced a switching to the orientation
is possible in a certain temperature and hole concentration range.Comment: 12 pages, 9 figure
Novel Quaternary Dilute Magnetic Semiconductor (Ga,Mn)(Bi,As): Magnetic and Magneto-Transport Investigations
Magnetic and magneto-transport properties of thin layers of the
(Ga,Mn)(Bi,As) quaternary dilute magnetic semiconductor grown by the
low-temperature molecular-beam epitaxy technique on GaAs substrates have been
investigated. Ferromagnetic Curie temperature and magneto-crystalline
anisotropy of the layers have been examined by using magneto-optical Kerr
effect magnetometry and low-temperature magneto-transport measurements.
Postgrowth annealing treatment has been shown to enhance the hole concentration
and Curie temperature in the layers. Significant increase in the magnitude of
magnetotransport effects caused by incorporation of a small amount of Bi into
the (Ga,Mn)As layers revealed in the planar Hall effect (PHE) measurements, is
interpreted as a result of enhanced spin-orbit coupling in the (Ga,Mn)(Bi,As)
layers. Two-state behaviour of the planar Hall resistance at zero magnetic
field provides its usefulness for applications in nonvolatile memory devices.Comment: 10 pages, 3 figures, to be published in the Proceedings of ICSM-2016
conferenc
Post-growth annealing of GaMnAs under As capping - an alternative way to increase Tc
We demonstrate that in situ post-growth annealing of GaMnAs layers under As
capping is adequate for achieving high Curie temperatures (Tc) in a similar way
as ex situ annealing in air or in N2 atmosphere practiced earlier.Comment: 13 pages, 4 figure
Entropy in Spin Foam Models: The Statistical Calculation
Recently an idea for computing the entropy of black holes in the spin foam
formalism has been introduced. Particularly complete calculations for the three
dimensional euclidean BTZ black hole were done. The whole calculation is based
on observables living at the horizon of the black hole universe. Departing from
this idea of observables living at the horizon, we now go further and compute
the entropy of BTZ black hole in the spirit of statistical mechanics. We
compare both calculations and show that they are very interrelated and equally
valid. This latter behaviour is certainly due to the importance of the
observables.Comment: 11 pages, 1 figur
Towards a spin foam model description of black hole entropy
We propose a way to describe the origin of black hole entropy in the spin
foam models of quantum gravity. This stimulates a new way to study the relation
of spin foam models and loop quantum gravity.Comment: 5 pages, 1 figur
Entropy of generic quantum isolated horizons
We review our recent proposal of a method to extend the quantization of
spherically symmetric isolated horizons, a seminal result of loop quantum
gravity, to a phase space containing horizons of arbitrary geometry. Although
the details of the quantization remain formally unchanged, the physical
interpretation of the results can be quite different. We highlight several such
differences, with particular emphasis on the physical interpretation of black
hole entropy in loop quantum gravity.Comment: 4 pages, contribution to loops '11 conference proceedings; 2
references added, a sentence remove
Diagnosis of major tumor categories in fine-needle aspirates is more accurate when light microscopy is combined with intermediate filament typing. A study of 403 cases.
Intermediate filament (IF) typing of tumor cells with monoclonal antibodies was applied to 403 fineneedle aspirates. In 271 cases specific cytologic diagnosis of tumor type was apparent from clinical data and light microscopic study alone. Intermediate filament typing confirmed the tumor type in 262 cases and changed an erroneous cytologic diagnosis of major tumor type in nine cases. In a second group of 132 difficult cases, where the tumor type could not be revealed with certainty, IF typing confirmed the cytologic suggestion of tumor type in 50 cases, changed it in nine cases, and helped resolve ambiguities in cytologic diagnosis in 59 cases. It did not help in 14 cases. Thus IF typing adds independent objective differentiation specific information to descriptive tumor typing currently used in aspiration cytologic study. When combined with the morphologic analysis of tumor cells and clinical information it can refine the cytologic diagnosis of major tumor types and prevent error
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