58 research outputs found
Magnetism in systems with various dimensionality: A comparison between Fe and Co
A systematic ab initio study is performed for the spin and orbital moments
and for the validity of the sum rules for x-ray magnetic circular dichroism for
Fe systems with various dimensionality (bulk, Pt-supported monolayers and
monatomic wires, free-standing monolayers and monatomic wires). Qualitatively,
the results are similar to those for the respective Co systems, with the main
difference that for the monatomic Fe wires the term in the spin sum rule
is much larger than for the Co wires. The spin and orbital moments induced in
the Pt substrate are also discussed.Comment: 4 page
Large Orbital Magnetic Moment and Coulomb Correlation effects in FeBr2
We have performed an all-electron fully relativistic density functional
calculation to study the magnetic properties of FeBr2. We show for the first
time that the correlation effect enhances the contribution from orbital degrees
of freedom of electrons to the total magnetic moment on Fe as
opposed to common notion of nearly total quenching of the orbital moment on
Fe site. The insulating nature of the system is correctly predicted when
the Hubbard parameter U is included. Energy bands around the gap are very
narrow in width and originate from the localized Fe-3 orbitals, which
indicates that FeBr2 is a typical example of the Mott insulator.Comment: 4 pages, 3 figures, revtex4, PRB accepte
Magnetic versus crystal field linear dichroism in NiO thin films
We have detected strong dichroism in the Ni x-ray absorption
spectra of monolayer NiO films. The dichroic signal appears to be very similar
to the magnetic linear dichroism observed for thicker antiferromagnetic NiO
films. A detailed experimental and theoretical analysis reveals, however, that
the dichroism is caused by crystal field effects in the monolayer films, which
is a non trivial effect because the high spin Ni ground state is not
split by low symmetry crystal fields. We present a practical experimental
method for identifying the independent magnetic and crystal field contributions
to the linear dichroic signal in spectra of NiO films with arbitrary
thicknesses and lattice strains. Our findings are also directly relevant for
high spin and systems such as LaFeO, FeO,
VO, LaCrO, CrO, and Mn manganate thin films
X-Ray Magnetic Circular Dichroism at the K edge of Mn3GaC
We theoretically investigate the origin of the x-ray magnetic circular
dichroism (XMCD) spectra at the K edges of Mn and Ga in the ferromagnetic phase
of Mn3GaC on the basis of an ab initio calculation. Taking account of the
spin-orbit interaction in the LDA scheme, we obtain the XMCD spectra in
excellent agreement with the recent experiment. We have analyzed the origin of
each structure, and thus elucidated the mechanism of inducing the orbital
polarization in the p symmetric states. We also discuss a simple sum rule
connecting the XMCD spectra with the orbital moment in the p symmetric states.Comment: 5 pages, 5 figures, accepted for publication in Physical Review
Nanosized superparamagnetic precipitates in cobalt-doped ZnO
The existence of semiconductors exhibiting long-range ferromagnetic ordering
at room temperature still is controversial. One particularly important issue is
the presence of secondary magnetic phases such as clusters, segregations,
etc... These are often tedious to detect, leading to contradictory
interpretations. We show that in our cobalt doped ZnO films grown
homoepitaxially on single crystalline ZnO substrates the magnetism
unambiguously stems from metallic cobalt nano-inclusions. The magnetic behavior
was investigated by SQUID magnetometry, x-ray magnetic circular dichroism, and
AC susceptibility measurements. The results were correlated to a detailed
microstructural analysis based on high resolution x-ray diffraction,
transmission electron microscopy, and electron-spectroscopic imaging. No
evidence for carrier mediated ferromagnetic exchange between diluted cobalt
moments was found. In contrast, the combined data provide clear evidence that
the observed room temperature ferromagnetic-like behavior originates from
nanometer sized superparamagnetic metallic cobalt precipitates.Comment: 20 pages, 6 figures; details about background subtraction added to
section III. (XMCD
Anisotropy of the orbital methods and the magnetic dipole term in : An {\it ab-initio} studt
A systematic study is performed by the {\it ab-initio} density functional
theory of the anisotropy of the orbital moments in bulk . Two different band-structure techniques are
used (FLAPW and LMTO-ASA), and the electronic correlations are treated by the
local-spin-density approximation (LSDA), the LSDA+ orbital polarization method,
and the LSDA+ method. The calculated anisotropies of are
very large compared to Fe, Ni and Co but still a factor of 5 and 2 smaller than
the anisotropies obtained from a recently suggested analysis of the X-ray
magnetic circular dichroism spectra for a thick layer of
A PKC-Dependent Recruitment of MMP-2 Controls Semaphorin-3A Growth-Promoting Effect in Cortical Dendrites
There is increasing evidence for a crucial role of proteases and metalloproteinases during axon growth and guidance. In this context, we recently described a functional link between the chemoattractive Sema3C and Matrix metalloproteinase 3 (MMP3). Here, we provide data demonstrating the involvement of MMP-2 to trigger the growth-promoting effect of Sema3A in cortical dendrites. The in situ analysis of MMP-2 expression and activity is consistent with a functional growth assay demonstrating in vitro that the pharmacological inhibition of MMP-2 reduces the growth of cortical dendrites in response to Sema3A. Hence, our results suggest that the selective recruitment and activation of MMP-2 in response to Sema3A requires a PKC alpha dependent mechanism. Altogether, we provide a second set of data supporting MMPs as effectors of the growth-promoting effects of semaphorins, and we identify the potential signalling pathway involved
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