6 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
Layered ferromagnet-superconductor structures: the state and proximity effects
We investigate clean mutilayered structures of the SFS and SFSFS type, (where
the S layer is intrinsically superconducting and the F layer is ferromagnetic)
through numerical solution of the self-consistent Bogoliubov-de Gennes
equations for these systems. We obtain results for the pair amplitude, the
local density of states, and the local magnetic moment. We find that as a
function of the thickness of the magnetic layers separating adjacent
superconductors, the ground state energy varies periodically between two stable
states. The first state is an ordinary "0-state", in which the order parameter
has a phase difference of zero between consecutive S layers, and the second is
a "-state", where the sign alternates, corresponding to a phase difference
of between adjacent S layers. This behavior can be understood from simple
arguments. The density of states and the local magnetic moment reflect also
this periodicity.Comment: 12 pages, 10 Figure
Controllаble Josephson 0–π Junction Based on a Four-Layer Ferromagnetic–Superconductor System (FSFS)
© 2020, Pleiades Publishing, Ltd. Abstract: A system containing four alternating ferromagnetic and superconducting layers (F1/S1/F2/S2) is examined in this work. The state of this contact may be controlled by an external magnetic field. The critical temperature of the superconducting transition and the Josephson current are calculated theoretically at different thicknesses and collinear orientations of magnetizations of ferromagnetic layers. It is demonstrated that this F1/S1/F2/S2 system may serve as a controllable Josephson 0–π contact or an inverse spin valve
Competition between BCS and FFLO States in Magnetic Superconductors in a Cryptoferromagnetic Phase
© 2020, Pleiades Publishing, Inc. The possibility of appearance of inhomogeneous superconducting Fulde—Ferrell—Larkin—Ovchinnikov (FFLO) states in magnetic superconductors in a cryptoferromagnetic phase with helical magnetic ordering has been analyzed. The dependence of the critical temperature on the angle between the wave vectors of the spatial modulation of the FFLO state and helical magnetic structure has been calculated within the proposed model. It has been shown that their mutually perpendicular orientation corresponds to the most energetically favorable state. The numerical calculations have also shown the existence of a tricritical point on a line separating the Bardeen—Cooper—Schrieffer and FFLO phases on the phase diagram of states. Furthermore, FFLO states can appear in a magnetic superconductor even at fairly strong exchange fields because of the difference between the effective masses of conduction electrons in different spin subbands and the anisotropy of the Fermi surface