155 research outputs found
Study of the crystal field in CeF<inf>3</inf> and CeF<inf>3</inf>:Pr<sup>3+</sup>
© Kazan Federal University (KFU).The crystal field analysis based on calculations in the framework of the semi phenomenological exchange charge model was carried out. The set of crystal field parameters for Ce3+ and Pr3+ ions in the matrix CeF3 related to the crystallographic system of coordinates has been obtained and used to reproduce satisfactory the crystal field energies of Ce3+ and Pr3+ ions
Memory Effect and Triplet Pairing Generation in the Superconducting Exchange Biased Co/CoOx/Cu41Ni59/Nb/Cu41Ni59 Layered Heterostructure
We fabricated a nanolayered hybrid superconductor-ferromagnet spin-valve
structure, the resistive state of which depends on the preceding magnetic field
polarity. The effect is based on a strong exchange bias (about -2 kOe) on a
diluted ferromagnetic copper-nickel alloy and generation of a long range odd in
frequency triplet pairing component. The difference of high and low resistance
states at zero magnetic field is 90% of the normal state resistance for a
transport current of 250 {\mu}A and still around 42% for 10 {\mu}A. Both logic
states of the structure do not require biasing fields or currents in the idle
mode.Comment: 9 pages, 4 figures, Accepted to Applied Physics Letter
Magnetoresistance of a semiconducting magnetic wire with domain wall
We investigate theoretically the influence of the spin-orbit interaction of
Rashba type on the magnetoresistance of a semiconducting ferromagnetic
nanostructure with a laterally constrained domain wall. The domain wall is
assumed sharp (on the scale of the Fermi wave length of the charge carriers).
It is shown that the magnetoresistance in such a case can be considerably
large, which is in a qualitative agreement with recent experimental
observations. It is also shown that spin-orbit interaction may result in an
increase of the magnetoresistance. The role of localization corrections is also
briefly discussed.Comment: 5 pages, 2 figure
Re-entrant superconductivity in Nb/Cu(1-x)Ni(x) bilayers
We report on the first observation of a pronounced re-entrant
superconductivity phenomenon in superconductor/ferromagnetic layered systems.
The results were obtained using a superconductor/ferromagnetic-alloy bilayer of
Nb/Cu(1-x)Ni(x). The superconducting transition temperature T_{c} drops sharply
with increasing thickness d_{CuNi} of the ferromagnetic layer, until complete
suppression of superconductivity is observed at d_{CuNi}= 4 nm. Increasing the
Cu(1-x)Ni(x) layer thickness further, superconductivity reappears at
d_{CuNi}=13 nm. Our experiments give evidence for the pairing function
oscillations associated with a realization of the quasi-one dimensional
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) like state in the ferromagnetic layer.Comment: 3 pages, 3 figures, REVTEX4/twocolum
Superconducting decay length in a ferromagnetic metal
The complex decay length xi characterizing penetration of superconducting
correlations into a ferromagnet due to the proximity effect is studied
theoretically in the frame of the linearized Eilenberger equations. The real
part xi_1 and imaginary part xi_2 of the decay length are calculated as
functions of exchange energy and the rates of ordinary, spin flip and spin
orbit electronic scattering in a ferromagnet. The lengths xi_1,2 determine the
spatial scales of, respectively, decay and oscillation of a critical current in
SFS Josephson junctions in the limit of large distance between superconducting
electrodes. The developed theory provides the criteria of applicability of the
expressions for xi_1 and xi_2 in the dirty and the clean limits which are
commonly used in the analysis of SF hybrid structures.Comment: 5 pages, 3 figure
Strain-induced magnetic anisotropies in epitaxial CrO2 thin films probed by FMR technique
Epitaxial CrO2 thin films were grown onto TiO2 (1 0 0) single-crystalline substrates by chemical vapour deposition (CVD) process with use of the solid precursor CrO3. The CrO2 films with thickness of 27 and 65 nm were deposited onto TiO2 substrates pre-etched in the diluted HF. The magnetic properties of the epitaxial chromium-dioxide films have been probed by the ferromagnetic resonance (FMR) technique. Analysis of the FMR spectra shows that the magnetic behaviour of the CrO2 films results from a competition between magnetocrystalline and strain anisotropies. The thin films are heavily strained due to lattice mismatch of CrO2 epitaxial film with the TiO2 single-crystalline substrate. For the thinnest film (27 nm) the stress anisotropy dominates, and the magnetic easy axis switches from the c direction to the b direction of the rutile structure. Unusual angular dependence of the resonance signal and multiple FMR modes are observed for the film with the thickness of 65 nm, where a partial strain relaxation results in appearance of two magnetic phases with mutually perpendicular easy axes along the c and b directions. © 2005 Elsevier B.V. All rights reserved
Influence of the film thickness and additional elements (Al, O, and N) on the properties of FeCo film structures
The magnetic properties and domain structure of FeCoAlON thin films with thicknesses varying from 55 to 550 nm have been studied, and conditions favoring preparation of FeCoAlON films with uniaxial anisotropy in the direction normal to the film plane, which is required for designing "perpendicular" super-high-density information recording, have been established. In FeCoAlON films with a thickness up to 300 nm, the domain structure consists of cross-linked domain walls, because strong demagnetizing field suppresses formation of stripe domains. After the film thickness has reached 320 nm, cross-linked domain walls transform into stripe domains, with uniaxial anisotropy in the film plane disappearing, to become replaced by uniaxial anisotropy in the direction normal to the film plane, which can be assigned to magnetoelastic stresses induced by nitrogen atoms filling up interstitial space in the (110) plane. A further increase in the film thickness (up to 550 nm) leads to a rotational anisotropy due to the increase of nitrogen concentration in interstitials and the increase of magnetoelastic stresses. © 2014 Pleiades Publishing, Ltd
Energy-Momentum Tensor of Field Fluctuations in Massive Chaotic Inflation
We study the renormalized energy-momentum tensor (EMT) of the inflaton
fluctuations in rigid space-times during the slow-rollover regime for chaotic
inflation with a mass term. We use dimensional regularization with adiabatic
subtraction and introduce a novel analytic approximation for the inflaton
fluctuations which is valid during the slow-rollover regime. Using this
approximation we find a scale invariant spectrum for the inflaton fluctuations
in a rigid space-time, and we confirm this result by numerical methods. The
resulting renormalized EMT is covariantly conserved and agrees with the
Allen-Folacci result in the de Sitter limit, when the expansion is exactly
linearly exponential in time. We analytically show that the EMT tensor of the
inflaton fluctuations grows initially in time, but saturates to the value H^2
H(0)^2, where H is the Hubble parameter and H(0) is its value when inflation
has started. This result also implies that the quantum production of light
scalar fields (with mass smaller or equal to the inflaton mass) in this model
of chaotic inflation depends on the duration of inflation and is larger than
the usual result extrapolated from the de Sitter result.Comment: revtex style, 24 pages, 6 eps figures Numerical checks added and
moduli section improve
Resistance of a domain wall in the quasiclassical approach
Starting from a simple microscopic model, we have derived a kinetic equation
for the matrix distribution function. We employed this equation to calculate
the conductance in a mesoscopic F'/F/F' structure with a domain wall (DW).
In the limit of a small exchange energy and an abrupt DW, the conductance
of the structure is equal to . Assuming that the scattering times
for electrons with up and down spins are close to each other we show that the
account for a finite width of the DW leads to an increase in this conductance.
We have also calculated the spatial distribution of the electric field in the F
wire. In the opposite limit of large (adiabatic variation of the
magnetization in the DW) the conductance coincides in the main approximation
with the conductance of a single domain structure . The account for rotation of
the magnetization in the DW leads to a negative correction to this conductance.
Our results differ from the results in papers published earlier.Comment: 11 pages; replaced with revised versio
Finite Temperature Effective Potential for Gauge Models in de Sitter Space
The one-loop effective potential for gauge models in static de Sitter space
at finite temperatures is computed by means of the --function method. We
found a simple relation which links the effective potentials of gauge and
scalar fields at all temperatures.
In the de Sitter invariant and zero-temperature states the potential for the
scalar electrodynamics is explicitly obtained, and its properties in these two
vacua are compared. In this theory the two states are shown to behave similarly
in the regimes of very large and very small radii a of the background space.
For the gauge symmetry broken in the flat limit () there is a
critical value of a for which the symmetry is restored in both quantum states.
Moreover, the phase transitions which occur at large or at small a are of the
first or of the second order, respectively, regardless the vacuum considered.
The analytical and numerical analysis of the critical parameters of the above
theory is performed. We also established a class of models for which the kind
of phase transition occurring depends on the choice of the vacuum.Comment: 23 pages, LaTeX, 5 figure.ep
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