137 research outputs found
Manipulating superconductivity through the domain structure of a ferromagnet: experimental aspects and theoretical implications
In the present work we study experimentally the influence that the domain
structure of a fer- romagnet (FM) has on the properties of a superconductor
(SC) in bilayers and multilayers of La0.60Ca0.40MnO3/Nb and FePt/Nb proximity
hybrids. Specific experimental protocols that were employed in the performed
magnetization measurements enabled us to directly uncover a generic property of
FM/SC hybrids: in the absence of an external magnetic field, the multidomain
struc- ture of the FM promotes the nucleation of superconductivity, while its
monodomain state strongly suppresses it. Our experimental findings support
recent theoretical studies proposing that when an inhomogeneous exchange field
is offered by the FM to the SC the superconducting pairs are not susceptible to
pair-breaking.Comment: 4 pages, 4 figure
Relaxation measurements in the regime of the second magnetization peak in Nb films
We report on magnetic measurements as a function of field, temperature and
time (relaxation) in superconducting Nb films of critical temperature Tc = 9.25
K. The magnetic measurements as a function of field exhibited a second
magnetization peak (SMP) which in general is accompanied by thermomagnetic
instabilities (TMIs). The lines where the SMP occurs and where the first flux
jump in the virgin magnetization curves is observed, end at a characteristic
point (To,Ho)=(7.2 K,80 Oe). Relaxation measurements showed that for T<To=7.2 K
the activation energy Uo and the normalized relaxation rate S exhibit
non-monotonic behavior as a function either of temperature or field. The
extrema observed in Uo and S coincide with the onset and the maximum points of
the SMP. In the regime T>To=7.2 K both Uo and S present a conventional
monotonic behavior. These results indicate that the SMP behavior observed in
our Nb films is promoted by the anomalous relaxation of the magnetization.Comment: To appear in Physica
Enhancement of Superconductivity by Exchange Bias
In this work we study the transport properties of hybrids that consist of
exchange biased ferromagnets (FMs) combined with a low-Tc superconductor (SC).
Not only different FMs but also various structural topologies have been
investigated: results for multilayers of La(1-x)CaxMnO3 combined with Nb in the
form of [La0.33Ca0.67MnO3/La0.60Ca0.40MnO3]15/Nb, and for more simple
Ni80Fe20/Nb/Ni80Fe20 trilayers and Ni80Fe20/Nb bilayers are presented. The
results obtained in all hybrid structures studied in this work clearly uncover
that the exchange bias mechanism promotes superconductivity. Our findings
assist the understanding of the contradictory results that have been reported
in the recent literature regarding the transport properties of relative
FM/SC/FM spin valves
Effective ferromagnetic coupling between a superconductor and a ferromagnet in LaCaMnO/Nb hybrids
In this work we present magnetization data on hybrids consisting of
multilayers (MLs) of man- ganites [La0.33Ca0.67MnO3/La0.60Ca0.40MnO3]15 in
contact with a low-Tc Nb superconductor (SC). Although a pure SC should behave
diamagnetically in respect to the external magnetic field in our ML-SC hybrids
we observed that the magnetization of the SC follows that of the ML. Our
intriguing experimental results show that the SC below its TSC c becomes
ferromagnetically coupled to the ML. As a result in the regime where
diamagnetic behaviour of the SC was expected its bulk magne- tization switches
only whenever the coercive field of the ML is exceeded. By employing specific
experiments where the ML was selectively biased or not we demonstrate that the
ML inflicts its magnetic properties on the whole hybrid. Possible explanations
are discussed in connection to recent theoretical proposals and experimental
findings that were obtained in relative hybrids.Comment: To appear in Phys. Rev.
Ferromagnetic-superconducting hybrid films and their possible applications: A direct study in a model combinatorial film
Model combinatorial films (CFs) which host a pure superconductor adjacent to
a ferromagneticsuperconducting hybrid film (HF) are manufactured for the study
of the influence of ferromagnetic nanoparticles (FNs) on the nucleation of
superconductivity. Careful resistance measurements were performed
simultaneously on two different sites of the CFs. Enhancement of
superconductivity and magnetic memory effects were observed only on the hybrid
site of the CFs but were absent on their purely superconducting part. Our
results give direct proof that the FNs modulate the superconducting order
parameter in an efficient and controlled way giving us the possibility of
miscellaneous practical applications.Comment: To appear in Physical Review
- …