350 research outputs found
Amplification of the induced ferromagnetism in diluted magnetic semiconductor
Magnetic properties of the planar structure consisting of a ferromagnetic
metal and the diluted magnetic semiconductor are considered (by the example of
the structure Fe/Ga(Mn)As, experimentally studied in [F. Maccherozzi, e.a.,
Phys. Rev. Lett., 101, 267201 (2008)]). In the framework of the mean field
theory, we demonstrate the presence of the significant amplification of the
ferromagnetism, induced by the ferromagnetic metal in the near-interface
semiconductor area, due to the indirect interaction of magnetic impurities.
This results in the substantial expansion of the temperature range where the
magnetization in the boundary semiconductor region exists, that might be
important for possible practical applications
Negative Magnetoresistance in Granular Bi - HTSC with Trapped Magnetic Fields
Magnetoresistive properties of granular Bi-based HTSC with trapped magnetic
fields are investigated in the temperature region near superconducting
transition . The effect of trapped field and transport current values and
orientations on the field dependence of magnetoresistance is studied. It is
found that for the magnetic field parallel and the current perpendicular to
trapping inducing field the field dependence of magnetoresistance is
nonmonotonic and magnetoresistance turns out to be negative for small fields.
The magnetoresistance sign inversion field increases roughly linear with the
trapped magnetic field and slightly decrease with transport current. The
results are explained in the framework of model of magnetic flux trapping in
granules or superconducting loops embedded in weak links matrix.Comment: 5 pages, 4 figures, submitted to conference LT2
Influence of chemical pressure effects on nonlinear thermal conductivity of intrinsically granular superconductors
Using a 2D model of capacitively coupled Josephson junction arrays (created
by a network of twin boundary dislocations with strain fields acting as an
insulating barrier between hole-rich domains in underdoped crystals), we study
the influence of chemical pressure on nonlinear thermal conductivity (NLTC) of
an intrinsically granular superconductor. Quite a substantial enhancement of
NLTC is predicted when intrinsic chemoelectric field closely matches the
externally produced thermoelectric field. The estimates of the model parameters
suggest a realistic possibility to experimentally monitor this effect in
non-stoichiometric superconductors.Comment: 10 pages, 2 figure
High frequency magnetic permeability of nanocomposite film
The high frequency magnetic permeability of nanocomposite film consisting of
the single-domain spherical ferromagnetic particles in the dielectric matrix is
studied. The permeability is assumed to be determined by rotation of the
ferromagnetic inclusion magnetic moments around equilibrium direction in AC
magnetic field. The composite is modeled by a cubic array of ferromagnetic
particles. The magnetic permeability tensor is calculated by solving the
Landau-Lifshits-Gilbert equation accounting for the dipole interaction of
magnetic particles. The permeability tensor components are found as functions
of the frequency, temperature, ferromagnetic inclusions density and magnetic
anisotropy. The obtained results show that nanocomposite films could have
rather high value of magnetic permeability in the microwave range
Quasi-Two Dimensional Diluted Magnetic Semiconductors with Arbitrary Carrier Degeneracy
In the framework of the generalized mean field theory, conditions for arising
the ferromagnetic state in a two-dimensional diluted magnetic semiconductor and
the features of that state are defined. RKKY-interaction of magnetic impurities
is supposed. The spatial disorder of their arrangement and temperature
alteration of the carrier degeneracy are taken into account
Thermomagnetic phenomena in the mixed state of high temperature superconductors
Galvano- and thermomagnetic-phenomena in high temperature superconductors, based on kinetic coefficients, are discussed, along with a connection between the electric field and the heat flow in superconductor mixed state. The relationship that determines the transport coefficients of high temperature superconductors in the mixed state based on Seebeck and Nernst effects is developed. It is shown that this relationship is true for a whole transition region of the resistive mixed state of a superconductor. Peltier, Ettingshausen and Righi-Leduc effects associated with heat conductivity as related to high temperature superconductors are also addressed
Magnetic properties of nanosized diluted magnetic semiconductors with band splitting
The continual model of the nonuniform magnetism in thin films and wires of a
diluted magnetic semiconductor is considered with taking into account the
finite spin polarization of carriers responsible for the indirect interaction
of magnetic impurities (e.g. via RKKY mechanism). Spatial distributions (across
the film thickness or the wire radius) of the magnetizaton and carrier
concentrations of different spin orientations, as well as the temperature
dependence of the average magnetization are determined as the solution of the
nonlinear integral equation
Curie Temperature for Small World Ising Systems of Different Dimensions
For Small World Ising systems of different dimensions, "concentration"
dependencies T_C(p) of the Curie temperature upon the fraction p of long-range
links have been derived on a basis of simple physical considerations. We have
found T_C(p) ~ 1/ln|p| for 1D, T_C(p) ~ p^{1/2} for 2D, and T_C(p) ~ p^{2/3}
for 3D.Comment: 3 pages, 2 figure
Conductance of Finite-Scale Systems with Multiple Percolation Channels
We investigate properties of two-dimensional finite-scale percolation systems
whose size along the current flow is smaller than the perpendicular size.
Successive thresholds of appearing multiple percolation channels in such
systems have been determined and dependencies of the conductance on their size
and percolation parameter have been calculated. Various experimental
examples show that the finite-scale percolation system is the natural
mathematical model suitable for the qualitative and quantitative description of
different physical systems.Comment: 11 pages, 7 figure
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