19 research outputs found
Adjustment of superconductivity and ferromagnetism in the few-layered ferromagnet–superconductor nanostructures
The phase diagrams of the few-layered nanosystems consisting of dirty superconducting (S) and
ferromagnetic (F) metals are investigated within the framework of the modern theory of the proximity
effect taking into account the boundary conditions. The F/S tetralayer and pentalayer are
shown to have considerably richer physics than the F/S bi- and trilayer (due to the interplay between
the 0 and π phase superconductivity and the 0 and π phase magnetism and nonequivalence of
layers) and even the F/S superlattices. It is proven that these systems can have different critical
temperatures and fields for different S layers. This predicted decoupled superconductivity is found
to manifest itself in its most striking way for F/S tetralayer. It is shown that F/S/F/S
tetralayer is the most perspective candidate for use in superconducting spin nanoelectronics
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.
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
Bosonic sector of the two-dimensional Hubbard model studied within a two-pole approximation
The charge and spin dynamics of the two-dimensional Hubbard model in the
paramagnetic phase is first studied by means of the two-pole approximation
within the framework of the Composite Operator Method. The fully
self-consistent scheme requires: no decoupling, the fulfillment of both Pauli
principle and hydrodynamics constraints, the simultaneous solution of fermionic
and bosonic sectors and a very rich momentum dependence of the response
functions. The temperature and momentum dependencies, as well as the dependency
on the Coulomb repulsion strength and the filling, of the calculated charge and
spin susceptibilities and correlation functions are in very good agreement with
the numerical calculations present in the literature
Uniform hopping approach to the FM Kondo Model at finite temperature
We study the ferromagnetic Kondo model with classical corespins via unbiased
Monte-Carlo simulations and derive a simplified model for the treatment of the
corespins at any temperature. Our simplified model captures the main aspects of
the Kondo model and can easily be evaluated both numerically and analytically.
It provides a better qualitative understanding of the physical features of the
Kondo model and rationalizes the Monte-Carlo results, including the spectral
density A_k(omega) of a 1D chain with nearest neighbor Coulomb repulsion. By
calculating the specific heat and the susceptibility of systems up to size
16^3, we determine the Curie temperature of the 3D one-orbital double-exchange
model, which agrees with experimental values.Comment: 11 pages, 9 figures, RevTex4, additional references cite
Proximity and Josephson effects in superconductor - antiferromagnetic Nb / \gamma-Fe50Mn50 heterostructures
We study the proximity effect in superconductor (S), antiferromagnetic (AF)
bilayers, and report the fabrication and measurement of the first trilayer
S/AF/S Josephson junctions. The disordered f.c.c. alloy \gamma-Fe50Mn50 was
used as the AF, and the S is Nb. Micron and sub-micron scale junctions were
measured, and the scaling of gives a coherence length in the AF of
2.4 nm, which correlates with the coherence length due to suppression of
in the bilayer samples. The diffusion constant for FeMn was found to be 1.7
\times 10 m s, and the density of states at the Fermi level was
also obtained. An exchange biased FeMn/Co bilayer confirms the AF nature of the
FeMn in this thickness regime.Comment: 6 pages, 5 figures, accepted for Phys. Rev.