412 research outputs found
Nature of magnetism in CaCoO
We find using LSDA+U band structure calculations that the novel
one-dimensional cobaltate CaCoO is not a ferromagnetic half-metal
but a Mott insulator. Both the octahedral and the trigonal Co ions are formally
trivalent, with the octahedral being in the low-spin and the trigonal in the
high-spin state. The inclusion of the spin-orbit coupling leads to the
occupation of the minority-spin orbital for the unusually coordinated
trigonal Co, producing a giant orbital moment (1.57 ). It also results
in an anomalously large magnetocrystalline anisotropy (of order 70 meV),
elucidating why the magnetism is highly Ising-like. The role of the oxygen
holes, carrying an induced magnetic moment of 0.13 per oxygen, for
the exchange interactions is discussed.Comment: 5 pages, 4 figures, and 1 tabl
Photoluminescence from low temperature grown InAs/GaAs quantum dots
The authors investigated a set of self-assembled InAs/GaAs quantum dots (QDs) formed by mol. beam epitaxy at low temp. (LT, 250 DegC) and postgrowth annealing. A QD photoluminescence (PL) peak around 1.01 eV was obsd. The PL efficiency quickly quenches between 6 and 40 K due to the tunneling out of the QD into traps within the GaAs barrier. The PL efficiency increases by a factor of 45-280 when exciting below the GaAs band gap, directly into the InAs QD layer. This points towards good optical quality QDs, which are embedded in a LT-GaAs barrier with a high trapping efficiency. [on SciFinder (R)
Spin-state transition in LaCoO3: direct neutron spectroscopic evidence of excited magnetic states
A gradual spin-state transition occurs in LaCoO3 around T~80-120 K, whose
detailed nature remains controversial. We studied this transition by means of
inelastic neutron scattering (INS), and found that with increasing temperature
an excitation at ~0.6 meV appears, whose intensity increases with temperature,
following the bulk magnetization. Within a model including crystal field
interaction and spin-orbit coupling we interpret this excitation as originating
from a transition between thermally excited states located about 120 K above
the ground state. We further discuss the nature of the magnetic excited state
in terms of intermediate-spin (IS, S=1) vs. high-spin (HS, S=2) states. Since
the g-factor obtained from the field dependence of the INS is g~3, the second
interpretation looks more plausible.Comment: 10 pages, 4 figure
Bubble transport by electro-magnetophoretic forces at anode bottom of aluminium cells
Electrically conducting and nonconducting particles and bubbles experience additional forcing in a liquid which carries electric current. These so called electro-magnetophoretic forces are well known in metallurgical applications, like metal purification in vacuum-arc remelting, electro-slag processes, impurity removal or
concentration change in special castings. However, the effect of electro-magnetophoretic forces has never been considered for aluminium cells where the gas bubbles evolving in the liquid electrolyte are surrounded by an electric current and significant magnetic fields. We present models to estimate the effect of electric current flow in the vicinity of the bubbles and the additional
pressure distribution resulting from the magnetic forces in the surrounding liquid electrolyte. According to the estimates, this force becomes important for bubbles exceeding 2 mm in size, and could be sufficient to overcome the typical drag force associated with electrolyte flow thereby opposing motion of the bubble along the base of the anode when it is inclined at a slight angle. The effect
could explain certain features of the anode effect onset.
Mathematical models and numerical results are presented and a further implementation in the general MHD code for the aluminium cell design is discussed
Nonlinear stabilization of tokamak microturbulence by fast ions
Nonlinear electromagnetic stabilization by suprathermal pressure gradients
found in specific regimes is shown to be a key factor in reducing tokamak
microturbulence, augmenting significantly the thermal pressure electromagnetic
stabilization. Based on nonlinear gyrokinetic simulations investigating a set
of ion heat transport experiments on the JET tokamak, described by Mantica et
al. [Phys. Rev. Lett. 107 135004 (2011)], this result explains the
experimentally observed ion heat flux and stiffness reduction. These findings
are expected to improve the extrapolation of advanced tokamak scenarios to
reactor relevant regimes.Comment: 5 pages, 5 figure
Bulk and surface electronic properties of SmB6: a hard x-ray photoelectron spectroscopy study
We have carried out bulk-sensitive hard x-ray photoelectron spectroscopy
(HAXPES) measurements on in-situ cleaved and ex-situ polished SmB6 single
crystals. Using the multiplet-structure in the Sm 3d core level spectra, we
determined reliably that the valence of Sm in bulk SmB6 is close to 2.55 at ~5
K. Temperature dependent measurements revealed that the Sm valence gradually
increases to 2.64 at 300 K. From a detailed line shape analysis we can clearly
observe that not only the J=0 but also the J=1 state of the Sm 4f 6
configuration becomes occupied at elevated temperatures. Making use of the
polarization dependence, we were able to identify and extract the Sm 4f
spectral weight of the bulk material. Finally, we revealed that the oxidized or
chemically damaged surface region of the ex-situ polished SmB6 single crystal
is surprisingly thin, about 1 nm only.Comment: 11 pages, 8 figure
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