129 research outputs found
Evidence for Induced Magnetization in Superconductor-Ferromagnet Hetero-structures: a Scanning Tunnelling Spectroscopy Study
We performed scanning tunneling spectroscopy of c-axis oriented YBCO films on
top of which ferromagnetic SRO islands were grown epitaxially in-situ. When
measured on the ferromagnetic islands, the density of states exhibits small
gap-like features consistent with the expected short range penetration of the
order parameter into the ferromagnet. However, anomalous split-gap structures
are measured on the superconductor in the vicinity of ferromagnetic islands.
This observation may provide evidence for the recently predicted induced
magnetization in the superconductor side of a superconductor/ ferromagnet
junction. The length scale of the effect inside the superconductor was found to
be an order of magnitude larger than the superconducting coherence length. This
is inconsistent with the theoretical prediction of a penetration depth of only
a few superconducting coherence lengths. We discuss a possible origin for this
discrepancy
Increasing the performance of the superconducting spin valve using a Heusler alloy
We have studied superconducting properties of the spin-valve thin layer
heterostructures CoO/F1/Cu/F2/Cu/Pb where the ferromagnetic F1 layer was
standardly made of Permalloy whereas for the F2 layer we have taken a specially
prepared film of the Heusler alloy CoCrFeAl with a small degree
of spin polarization of the conduction band. The heterostructures demonstrate a
significant superconducting spin-valve effect, i.e. a complete switching on and
off of the superconducting current flowing through the system by manipulating
the mutual orientations of the magnetization of the F1 and F2 layers. The
magnitude of the effect is doubled in comparison with the previously studied
analogous multilayers with the F2 layer made of the strong ferromagnet Fe.
Theoretical analysis shows that a drastic enhancement of the switching effect
is due to a smaller exchange field in the heterostructure coming from the
Heusler film as compared to Fe. This enables to approach almost ideal
theoretical magnitude of the switching in the Heusler-based multilayer with the
F2 layer thickness of \,nm
Experimental Observation of the Inverse Proximity Effect in Superconductor/Ferromagnet Layered Structures
We have studied the nuclear magnetic resonance (NMR) of 51V nuclei in the
superconductor/ferromagnet thin film heterostructures Ni/V/Ni and
Pd{1-x}Fe{x}/V/Pd{1-x}Fe{x} in the normaland superconducting state. Whereas the
position and shape of the NMR line in the normal state for the trilayers is
identical to that observed in a single V-layer, in the superconducting state
the line shape definitely changes, developing a systematic distortion of the
high-field wing of the resonance line. We consider this as the first
experimental evidence for the penetration of ferromagnetism into the
superconducting layer, a phenomenon which has been theoretically predicted
recently and dubbed the inverse proximity effect.Comment: about 5 pages, 3 figures, 1 tabl
Manifestation of New Interference Effects in Superconductor/Ferromagnet Spin Valve
Superconductor/ferromagnet (S/F) spin valve effect theories based on the S/F
proximity phenomenon assume that the superconducting transition temperature Tc
of F1/F2/S or F1/S/F2 trilayers for parallel magnetizations of the F1- and
F2-layers (TcP) are smaller than for the antiparallel orientations (TcAP).
Here, we report for CoOx/Fe1/Cu/Fe2/In multilayered systems with varying
Fe2-layer thickness the sign-changing oscillating behavior of the spin valve
effect \Delta Tc=TcAP-TcP. Our measurements revealed the full direct spin valve
effect with TcAP>TcP for Fe2-layer thickness dFe2<1 nm and the full inverse
(TcAP=1 nm. Interference of Cooper pair wave
functions reflected from both surfaces of the Fe2-layer appear as the most
probable reason for the observed behavior of \Delta Tc.Comment: Accepted for publication in PR
Method of investigation of deformations of solids of incompressible materials
© Published under licence by IOP Publishing Ltd.The aim of this work is development mathematical models, algorithm for the investigation stress-strain state of elastic solids, taking into account the incompressibility materials. The constitutive equations are received using a potential energy of deformations. The system of the linear algebraic equations is received by linearization of a resolving equation. The penalty method is applied for a modelling of the incompressibility of the material. The finite element method is used for numerical solution of the problems
Spin Screening and Antiscreening in a Ferromagnet/Superconductor Heterojunction
We present a theoretical study of spin screening effects in a
ferromagnet/superconductor (F/S) heterojunction. It is shown that the magnetic
moment of the ferromagnet is screened or antiscreened, depending on the
polarization of the electrons at the Fermi level. If the polarization is
determined by the electrons of the majority (minority) spin band then the
magnetic moment of the ferromagnet is screened (antiscreened) by the electrons
in the superconductor. We propose experiments that may confirm our theory: for
ferromagnetic alloys with certain concentration of Fe or Ni ions there will be
screening or antiscreening respectively. Different configurations for the
density of states are also discussed.Comment: 5 pages; 4 figures. to be published in Phys. Rev,
Oscillations of Induced Magnetization in Superconductor-Ferromagnet Heterostructures
We study a change in the spin magnetization of a superconductor-ferromagnet
(SF) heterostructure, when temperature is lowered below the superconducting
transition temperature. It is assumed that the SF interface is smooth on the
atomic scale and the mean free path is not too short. Solving the Eilenberger
equation we show that the spin magnetic moment induced in the superconductor is
an oscillating sign-changing function of the product of the exchange field
and the thickness of the ferromagnet. Therefore the total spin magnetic
moment of the system in the superconducting state can be not only smaller
(screening) but also greater (anti-screening) than that in the normal state, in
contrast with the case of highly disordered (diffusive) systems, where only
screening is possible. This surprising effect is due to peculiar periodic
properties of localized Andreev states in the system. It is most pronounced in
systems with ideal ballistic transport (no bulk disorder in the samples, smooth
ideally transparent interface), however these ideal conditions are not crucial
for the very existence of the effect. We show that oscillations exist (although
suppressed) even for arbitrary low interface transparency and in the presence
of bulk disorder, provided that ( -- mean free path). At
low interface transparency we solve the problem for arbitrary strength of
disorder and obtain oscillating magnetization in ballistic regime () and nonoscillating magnetization in diffusive one () as
limiting cases of one formula.Comment: 10 pages, 2 figures, accepted for publication in Phys. Rev.
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