2,232 research outputs found
Magnetoelectric Properties of (CaSr)CoSiO Crystals
We have investigated the magnetoelectric properties of
(CaSr)CoSiO () crystals with a
quasi-two-dimensional structure. In CaCoSiO (), a canted
antiferromagnetic transition occurs at 5.6 K. The transition temperature
is increasing with increasing Sr concentration, and the rises of
the magnetization and dielectric constant become larger. Since the dielectric
constant shows large change at and the magnetocapacitance effect is
observed below , a coupling between the magnetism and dielectricity
is strong in (CaSr)CoSiO. The positive
magnetocapacitance is reduced by Sr substitution, and is not observed in . Namely, the compound of does not show the
magnetic-field-induced electric polarization. On the other hand, the negative
magnetocapacitance is enhanced by Sr substitution.Comment: 4 pages, 2figures, proceeding of International Conference on
Magnetism 200
Phase equilibrium in two orbital model under magnetic field
The phase equilibrium in manganites under magnetic field is studied using a
two orbital model, based on the equivalent chemical potential principle for the
competitive phases. We focus on the magnetic field induced melting process of
CE phase in half-doped manganites. It is predicted that the homogenous CE phase
begins to decompose into coexisting ferromagnetic phase and CE phase once the
magnetic field exceeds the threshold field. In a more quantitative way, the
volume fractions of the two competitive phases in the phase separation regime
are evaluated.Comment: 4 pages, 4 figure
Scanning tunneling microscopy and spectroscopy of the electronic local density of states of graphite surfaces near monoatomic step edges
We measured the electronic local density of states (LDOS) of graphite
surfaces near monoatomic step edges, which consist of either the zigzag or
armchair edge, with the scanning tunneling microscopy (STM) and spectroscopy
(STS) techniques. The STM data reveal that the and honeycomb superstructures coexist over a length scale of 3-4 nm
from both the edges. By comparing with density-functional derived nonorthogonal
tight-binding calculations, we show that the coexistence is due to a slight
admixing of the two types of edges at the graphite surfaces. In the STS
measurements, a clear peak in the LDOS at negative bias voltages from -100 to
-20 mV was observed near the zigzag edges, while such a peak was not observed
near the armchair edges. We concluded that this peak corresponds to the
graphite "edge state" theoretically predicted by Fujita \textit{et al.} [J.
Phys. Soc. Jpn. {\bf 65}, 1920 (1996)] with a tight-binding model for graphene
ribbons. The existence of the edge state only at the zigzag type edge was also
confirmed by our first-principles calculations with different edge
terminations.Comment: 20 pages, 11 figure
Gigantic magnetoelectric effect caused by magnetic-field-induced canted antiferromagnetic-paramagnetic transition in quasi-two-dimensional CaCoSiO crystal
We have investigated the magnetic and dielectric properties of
CaCoSiO crystal. The dielectricity and magnetism of
CaCoSiO are strongly coupled below a canted antiferromagnetic
transition temperature (): Magnetic fields induce electric
polarization below . Interestingly, the magnetic-field-induced
electric polarization is detected even without poling electric fields. Below
, a canted antiferromagnetic-paramagnetic transition is induced by
magnetic fields. The large magnetocapacitance is observed around .
The origin of the large magnetocapacitance is due to the magnetic-field-induced
the canted antiferromagnetic-paramagnetic transition.Comment: 3 pages, 3 figures. accepted to Applied Physics Letter
Electronic structure theory of the hidden order material URuSi
We report a comprehensive electronic structure investigation of the
paramagnetic (PM), the large moment antiferromagnetic (LMAF), and the hidden
order (HO) phases of URuSi. We have performed relativistic
full-potential calculations on the basis of the density functional theory
(DFT), employing different exchange-correlation functionals to treat electron
correlations within the open -shell of uranium. Specifically, we
investigate---through a comparison between calculated and low-temperature
experimental properties---whether the electrons are localized or
delocalized in URuSi. We also performed dynamical mean field theory
calculations (LDA+DMFT) to investigate the temperature evolution of the
quasi-particle states at 100~K and above, unveiling a progressive opening of a
quasi-particle gap at the chemical potential when temperature is reduced. A
detailed comparison of calculated properties with known experimental data
demonstrates that the LSDA and GGA approaches, in which the uranium
electrons are treated as itinerant, provide an excellent explanation of the
available low-temperature experimental data of the PM and LMAF phases. We show
furthermore that due to a materials-specific Fermi surface instability a large,
but partial, Fermi surface gapping of up to 750 K occurs upon antiferromagnetic
symmetry breaking. The occurrence of the HO phase is explained through
dynamical symmetry breaking induced by a mode of long-lived antiferromagnetic
spin-fluctuations. This dynamical symmetry breaking model explains why the
Fermi surface gapping in the HO phase is similar but smaller than that in the
LMAF phase and it also explains why the HO and LMAF phases have the same Fermi
surfaces yet different order parameters. Suitable derived order parameters for
the HO are proposed to be the Fermi surface gap or the dynamic spin-spin
correlation function.Comment: 23 pages, 20 figure
Dimensional Crossover driven by Magnetic Ordering in Optical Conductivity of Pr_{1/2}Sr_{1/2}MnO_3
We investigated optical properties of Pr_{0.5}Sr_{0.5}MnO_3, which has the
A-type antiferromagnetic ordering at a low temperature. We found that T-
dependence of spectral weight transfer shows a clear correlation with the
magnetic phase transition. In comparison with the optical conductivity results
of Nd_{0.5}Sr_{0.5}MnO_3, which has the CE-type antiferromagnetic charge
ordering, we showed that optical properties of Pr_{0.5}Sr_{0.5}MnO_3 near the
Neel temperature could be explained by a crossover from 3D to 2D metals.
Details of spectral weight changes are consistent with the polaron picture.Comment: 11 pages, 4 figures, submitted to PRL at June
On the Mechanisms of Haemodialysis-induced Neutropenia: A Study with Five New and Re-used Membranes
A prospective study was undertaken in 12 haemodialysed patients successively treated on five new as well as re-used dialyser membranes, that is cuprophane, cellulose acetate, polysulphone, polycarbonate, and polyacrylonitrile. A significant reduction of neutrophils occurred with every membrane during their first use, which improved only with cuprophane upon re-use. Thrombocytopenia was noted only when neutropenia reached very low values. Monocyte reduction occurred on cuprophane, cellulose acetate and polycarbonate, but did not improve during second use. C3d accumulation paralleled the time course of neutropenia only with cuprophane and cellulose acetate. Plasma collected at the extreme of neutropenia induced aggregation of control and predialysis cells, but did not aggregate autologous dialysed neutrophils collected at 5 min. Our data indicate that the mechanism linking complement activation to neutropenia is probably triggered by more than one facto
Validação de um método para detecção e quantificação de soja culticance tolerante a herbicidas imidazolinonas por PCR convencional e quantitativo.
bitstream/item/71972/1/ID-30956.pd
Relations between structural distortions and transport properties in NdCaMnO strained thin films
Strained thin films of charge/orbital ordered (CO/OO)
(NCMO) with various thickness have grown on (100)-SrTiO and (100)-LaAlO
substrates, by using the Pulsed Laser Deposition (PLD) technique. The thickness
of the films influences drastically the transport properties. As the thickness
decreases, the CO transition increases while at the same time the
insulator-to-metal transition temperature decreases under application of a 7T
magnetic field. Clear relationships between the structural distortions and the
transport properties are established. They are explained on the basis of the
elongation and the compression of the Mn-O-Mn and Mn-O bond angles and
distances of the \QTR{it}{Pnma} structure, which modify the bandwidth and the
Jahn-Teller distortion in these materialsComment: 11 pages, 6 figures. to be published in Journal Physics: Condensed
Matte
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