34 research outputs found
Thermodynamic properties of ferromagnetic/superconductor/ferromagnetic nanostructures
The theoretical description of the thermodynamic properties of
ferromagnetic/superconductor/ferromagnetic (F/S/F) systems of nanoscopic scale
is proposed. Their superconducting characteristics strongly depend on the
mutual orientation of the ferromagnetic layers. In addition, depending on the
transparency of S/F interfaces, the superconducting critical temperature can
exhibit four different types of dependences on the thickness of the F-layer.
The obtained results permit to give some practical recommendations for the
spin-valve effect experimental observation. In this spin-valve sandwich, we
also expect a spontaneous transition from parallel to anti-parallel
ferromagnetic moment orientation, due to the gain in the superconducting
condensation energy.Comment: 20 pages, 5 figures, submitted to PR
Strabon dans la vie et l'oeuvre de Coray
[Δεν διατίθεται περίληψη / no abstract available]No abstrac
Strabon dans la vie et l'oeuvre de Coray
[Δεν διατίθεται περίληψη / no abstract available]No abstrac
Theoretical description of the ferromagnetic -junctions near the critical temperature
The theory of ferromagnetic Pi-junction near the critical temperature is
presented. It is demonstrated that in the dirty limit the modified Usadel
equation adequately describes the proximity effect in ferromagnets. To provide
the description of an experimentally relevant situation, oscillations of the
Josephson critical current are calculated as a function of ferromagnetic layer
thickness for different transparencies of the superconductor-ferromagnet
interfaces.Comment: 12 pages, 4 figures, submitted to Phys. Rev.
Local Density of States and Order Parameter Configurations in Layered Ferromagnet-Superconductor Structures
We analyze the local density of states (LDOS) of heterostructures consisting
of alternating ferromagnet, , and superconductor, , layers. We consider
structures of the and type, with thin nanometer scale and
layers, within the ballistic regime. The spin-splitting effects of the
ferromagnet and the mutual coupling between the regions, yield several
nontrivial stable and metastable pair amplitude configurations, and we find
that the details of the spatial behavior of the pair amplitude govern the
calculated electronic spectra. These are reflected in discernible signatures of
the LDOS. The roles that the magnetic exchange energy, interface scattering
strength, and the Fermi wavevector mismatch each have on the LDOS for the
different allowed junction configurations, are systematically investigated.Comment: 20 pages, 10 figures. Figures are screen captures, high resolution
figures are available from either autho
Theory of proximity effect in superconductor/ferromagnet heterostructures
We present a microscopic theory of proximity effect in the
ferromagnet/superconductor/ferromagnet (F/S/F) nanostructures where S is s-wave
low-T_c superconductor and F's are layers of 3d transition ferromagnetic metal.
Our approach is based on the solution of Gor'kov equations for the normal and
anomalous Green's functions together with a self-consistent evaluation of the
superconducting order parameter. We take into account the elastic
spin-conserving scattering of the electrons assuming s-wave scattering in the S
layer and s-d scattering in the F layers. In accordance with the previous
quasiclassical theories, we found that due to exchange field in the ferromagnet
the anomalous Green's function F(z) exhibits the damping oscillations in the
F-layer as a function of distance z from the S/F interface. In the given model
a half of period of oscillations is determined by the length \xi_m^0 = \pi
v_F/E_ex, where v_F is the Fermi velocity and E_ex is the exchange field, while
damping is governed by the length l_0 = (1/l_{\uparrow} +
1/l_{\downarrow})^{-1} with l_{\uparrow} and l_{\downarrow} being
spin-dependent mean free paths in the ferromagnet. The superconducting
transition temperature T_c(d_F) of the F/S/F trilayer shows the damping
oscillations as a function of the F-layer thickness d_F with period \xi_F =
\pi/\sqrt{m E_ex}, where m is the effective electron mass. We show that strong
spin-conserving scattering either in the superconductor or in the ferromagnet
significantly suppresses these oscillations. The calculated T_c(d_F)
dependences are compared with existing experimental data for Fe/Nb/Fe trilayers
and Nb/Co multilayers.Comment: 13 pages, REVTeX4, 8 PS-figures; improved version, submitted to PR
Decoupling of superconducting layers in magnetic superconductor RuSr_{2}GdCu_{2}O_{8}
We propose the model for magnetic properties of the magnetic superconductor
RuSrGdCuO, which incorporates the theory of the
superconducting/ferromagnetic multilayers. The transition line , on
which the Josephson coupled superconducting planes are decoupled, i.e. , is calculated as a function of the exchange energy . As the
result of this decoupling a nonmonotonic behavior of magnetic properties, like
the lower critical field , Josephson plasma frequency, etc. is realized
near (or by crossing) the line. The obtained results are used in
analyzing the newly discovered antiferromagnetic ruthenocuprate
RuSrGdCuO with possible weak ferromagnetic order in the RuO
planes.Comment: 12 pages, 3 figs embede
Crossed Andreev reflection at ferromagnetic domain walls
We investigate several factors controlling the physics of hybrid structures
involving ferromagnetic domain walls (DWs) and superconducting (S) metals. We
discuss the role of non collinear magnetizations in S/DW junctions in a spin
Nambu Keldysh formalism. We discuss transport in S/DW/N and
S/DW/S junctions in the presence of inelastic scattering in the domain wall. In
this case transport properties are similar for the S/DW/S and S/DW/N junctions
and are controlled by sequential tunneling of spatially separated Cooper pairs
across the domain wall. In the absence of inelastic scattering we find that a
Josephson current circulates only if the size of the ferromagnetic region is
smaller than the elastic mean free path meaning that the Josephson effect
associated to crossed Andreev reflection cannot be observed under usual
experimental conditions. Nevertheless a finite dc current can circulate across
the S/DW/S junction due to crossed Andreev reflection associated to sequential
tunneling.Comment: 18 pages, 8 figures, references added at the end of the introductio
Proximity effects at ferromagnet-superconductor interfaces
We study proximity effects at ferromagnet superconductor interfaces by
self-consistent numerical solution of the Bogoliubov-de Gennes equations for
the continuum, without any approximations. Our procedures allow us to study
systems with long superconducting coherence lengths. We obtain results for the
pair potential, the pair amplitude, and the local density of states. We use
these results to extract the relevant proximity lengths. We find that the
superconducting correlations in the ferromagnet exhibit a damped oscillatory
behavior that is reflected in both the pair amplitude and the local density of
states. The characteristic length scale of these oscillations is approximately
inversely proportional to the exchange field, and is independent of the
superconducting coherence length in the range studied. We find the
superconducting coherence length to be nearly independent of the ferromagnetic
polarization.Comment: 13 Pages total. Compressed .eps figs might display poorly, but will
print fin
La géographie historique de la Grèce antique au XVIIe siècle à Caen
Baladié Raoul. La géographie historique de la Grèce antique au XVIIe siècle à Caen. In: Journal des savants, 1996, n°1. pp. 161-259