96 research outputs found
Processing line for industrial radiation-thermal synthesis of doped lithium ferrite powders
The paper considers the issues of industrial production of doped lithium ferrite powders by radiation-thermal method. A technological scheme of the processing line is suggested. The radiation-thermal technological scheme enables production of powders with technical characteristics close to the required ones under relatively low temperature annealing conditions without intermediate mixing. The optimal conditions of the radiation-thermal synthesis are achieved isothermally under irradiation by the electron beam with energy of 2.5 MeV in the temperature range of 700-750 °С within~ 120 min
Generalized kinetic equations for charge carriers in graphene
A system of generalized kinetic equations for the distribution functions of
two-dimensional Dirac fermions scattered by impurities is derived in the Born
approximation with respect to short-range impurity potential. It is proven that
the conductivity following from classical Boltzmann equation picture, where
electrons or holes have scattering amplitude reduced due chirality, is
justified except for an exponentially narrow range of chemical potential near
the conical point. When in this range, creation of infinite number of
electron-hole pairs related to quasi-relativistic nature of electrons in
graphene results in a renormalization of minimal conductivity as compared to
the Boltzmann term and logarithmic corrections in the conductivity similar to
the Kondo effect.Comment: final version, Phys. Rev. B, accepte
Spin Wave Theory of Double Exchange Ferromagnets
We construct the 1/S spin-wave expansion for double exchange ferromagnets at
T=0. It is assumed that the value of Hund's rule coupling, J_H, is sufficiently
large, resulting in a fully saturated, ferromagnetic half-metallic ground
state. We evaluate corrections to the magnon dispersion law, and we also find
that, in contrast to earlier statements in the literature, magnon-electron
scattering does give rise to spin wave damping. We analyse the momentum
dependence of these quantities and discuss the experimental implications for
colossal magnetoresistance compounds.Comment: 4 pages, Latex-Revtex, 2 PostScript figures. Minor revisions,
references added. See also cond-mat/990921
Scaling picture of magnetism formation in the anomalous f-systems: interplay of the Kondo effect and spin dynamics
Formation of magnetically ordered state in the Kondo lattices is treated
within the degenerate exchange and Coqblin-Schrieffer models. The Kondo
renormalizations of the effective coupling parameter, magnetic moment and spin
excitation frequencies are calculated within perturbation theory. The results
of one-loop scaling consideration of the magnetic state in Kondo lattices are
analyzed. The dependence of the critical values of the bare model parameters on
the type of the magnetic phase and space dimensionality is investigated.
Renormalization of the effective Kondo temperature by the interatomic exchange
interactions is calculated. An important role of the character of spin dynamics
(existence of well-defined magnon excitations, presence of magnetic anisotropy
etc.) is demonstrated. The regime of strongly suppressed magnetic moments,
which corresponds to magnetic heavy-fermion system, may occur in a rather
narrow parameter region only. At the same time, in the magnetically ordered
phases the renormalized Kondo temperature depends weakly on the bare coupling
parameter in some interval. The critical behavior, corresponding to the
magnetic transition with changing the bare coupling parameter, is
investigated. In the vicinity of the strong coupling regime, the spectrum of
the Bose excitations becomes softened. Thus on the borderline of magnetic
instability the Fermi-liquid picture is violated in some temerature interval
due to scattering of electrons by these bosons. This may explain the fact that
a non-Fermi-liquid behavior often takes place in the heavy-fermion systems near
the onset of magnetic ordering.Comment: 20 pages, RevTeX, 13 figure
Rho-Omega Mixing and the Pion Form Factor in the Time-like Region
We determine the magnitude, phase, and -dependence of -
``mixing'' in the pion form factor in the time-like region through fits to
e^+e^- \ra \pi^+ \pi^- data. The associated systematic errors in these
quantities, arising from the functional form used to fit the resonance,
are small. The systematic errors in the mass and width, however, are
larger than previously estimated.Comment: 20 pages, REVTeX, epsfig, 2 ps figures, minor change
Colossal magnetoresistance and quenched disorder in manganese oxides
We give an overview on several recent topics of colossal magnetoresistive
manganites in both experiments and theories, focusing on the effect of quenched
disorder. The disorder is intrinsically involved since the compounds are solid
solutions, and its importance has been pointed out in several experiments of
transport and magnetic properties. Recent progress in the experimental control
of the strength of disorder is also reviewed. Theoretically, the effect of the
disorder has been explored within the framework of the double-exchange
mechanism. Several efforts to understand the phase diagram and the electronic
properties are reviewed. We also briefly discuss a recent topic on the effect
of disorder on competing phases and the origin of colossal magnetoresistance.Comment: 5 pages, 4 figures, proceedings submitted to SPQS200
Study of the process in the energy region 400<\sqrt[]{s}<1000 MeV
The cross section of the process e^+e^-\to \pi^+\pi^- was measured in the SND
experiment at the VEPP-2M collider in the energy region 400<\sqrt[]{s}<1000
MeV. This measurement was based on about 12.4 \times 10^6 selected collinear
events, which include 7.4\times 10^6 e^+e^-\to e^+e^-, 4.5\times 10^6
e^+e^-\to\pi^+\pi^- and 0.5\times 10^6 e^+e^-\to\mu^+\mu^- selected events. The
systematic uncertainty of the cross section determination is 1.3 %. The
\rho-meson parameters were determined: m_\rho=774.9\pm 0.4\pm 0.5 MeV,
\Gamma_\rho=146.5\pm 0.8\pm 1.5 MeV, \sigma(\rho\to\pi^+\pi^-)=1220\pm 7\pm 16
nb as well as the parameters of the G-parity suppressed decay
\omega\to\pi^+\pi^-: \sigma(\omega\to\pi^+\pi^-)=29.9\pm 1.4\pm 1.0 nb and
\phi_{\rho\omega} = 113.5\pm 1.3\pm 1.7 degree.Comment: 30 pages REVTEX and 31 figure
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