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 La1−xCaxMnO3 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.

In this work we report on the transport and magnetic properties of hybrid trilayers (TLs) and bilayers (BLs) that consist of low spin polarized Ni80Fe20 exhibiting in-plane but no uniaxial anisotropy and low-Tc Nb. We reveal a magnetoresistance effect of magnitude identical to the one's that were reported in [V. Peña et al., Phys. Rev. Lett. 94, 57002 (2005)] for TLs consisting of highly spin polarized La0.7Ca0.3MnO3 and high-Tc YBa2Cu3O7. The presented effect is pronounced when compared to the one reported in [A.Yu. Rusanov et al., Phys. Rev. B 73, 060505(R) (2006)] for Ni80Fe20-Nb-Ni80Fe20 TLs of strong in-plane uniaxial anisotropy. In our TLs the magnetoresistance exhibits an increase of two orders of magnitude when the superconducting state is reached: from the conventional normal-state values ∆R/Rnor × 100% = 0.6% it goes up to ∆R/Rnor × 100% = 45% (∆R/Rmin × 100% = 1000%) for temperatures below T SC c . In contrast, in the BLs the effect is only minor since from ∆R/Rnor×100% = 3% in the normal state increases only to ∆R/Rnor×100% = 8% (∆R/Rmin × 100% = 70%) for temperatures below T SC c . Magnetization data of both the longitudinal and transverse magnetic components are presented. Most importantly, in this work we present data not only for the normal state of Nb but also in its superconducting state. Strikingly, these data show that below its T SC c the Nb interlayer under the influence of the outer Ni80Fe20 layers attains a magnetization component transverse to the external field. By comparing the transport and magnetization data we propose a new candidate mechanism that could motivate the pronounced magnetoresistance effect observed in the TLs. Adequate magnetostatic coupling of the outer Ni80Fe20 layers is motivated by stray fields that emerge naturally in their whole surface due to the multidomain magnetic structure that they attain near coercivity. Consequently, the stray fields penetrate the Nb interlayer and suppress its superconducting properties by primarily (secondarily) exceeding its lower (upper) critical field. Atomic force microscopy is employed in order to examine the possibility that such magnetostatic coupling could be promoted by interface roughness. Referring to the BLs, although out-of-plane rotation of the single Ni80Fe20 layer is still observed, in these structures magnetostatic coupling doesn't occur due to the absence of a second Ni80Fe20 one so that the observed magnetoresistance peaks are only modest.

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.PACS numbers: 74.25. Fy, 74.78.Fk, 85.25.Hv Ferromagnetic-superconducting hybrid systems where magnetism coexists with superconductivity have been the subject of intensive theoretical studies for many years.1,2,3,4 Advances in fabrication techniques have recently enabled the reliable preparation of such systems mainly in the form of HFs. 5,6,7,8,9,10,11,12 Probably the HF which is most widely studied by recent experiments is the one consisting of ordered or randomly distributed FNs embedded in a superconducting layer. 5,6,7,8,9,10,11,12 The most prominent effect that the FNs impose on the superconductor is the controlled modulation of the superconducting order parameter. Under specific conditions superconductivity in a HF may survive (or can be destroyed) at temperatures or magnetic fields higher (lower) than that observed in a single superconductor. 5,6,7,8,10,12 In most studies transport measurements were mainly employed to probe the superconducting fraction of the HF. It was observed that under certain conditions, depending mainly on the alignment of the FNs, the resistance in the HF maintained a lower value than the one observed in a reference pure superconducting layer. Most of the studies attributed the lowering of the measured resistance to the enhancement of the bulk and/or the surface critical current that the superconductor may sustain. 5,6,7,8,9,10,11,12 This specific property makes HFs important for power applications. Except for current-carrying applications HFs could be also useful as prototypes for the design of magnetoresistive memory devices or superconductive spin valves. 13,14,15,16 In the near future such devices could serve as data storage elements in a similar way to other candidate devices which are based on different physical mechanisms (for example giant magnetoresistance elemental devices).In this work we study the nucleation of superconductivity in model CFs which are constructed by CoPt FNs and a high quality layer of Nb superconductor. Nb and CoPt FNs were chosen as the ingredients of the CFs since their respective superconducting and magnetic properties are well studied and can be modified in a controlled way by altering the preparation conditions during sputtering and subsequent annealing. 7,8,17,18,19 The FNs employed in this work are anisotropic with their easy-axiŝ a e of magnetization nor...

It is generally believed that superconductivity and magnetism are two antagonistic long-range phenomena. However, as it was preliminarily highlighted in D. Stamopoulos et al. [Phys. Rev. B 75, 014501 (2007)] and extensively studied in this work under specific circumstances these phenomena instead of being detrimental to each other may even become cooperative so that their synergy may promote the superconducting properties of a hybrid structure.Here, we have studied systematically the magnetic and transport behavior of such exchange biased hybrids that are comprised of ferromagnetic (FM) Ni80Fe20 and low-Tc superconducting (SC) Nb for the case where the magnetic field is applied parallel to the specimens. Two structures have been studied: FM-SC-FM trilayers (TLs) and FM-SC bilayers (BLs). Detailed magnetization data on the longitudinal and transverse magnetic components are presented for both the normal and superconducting states. These data are compared to systematic transport measurements including I-V characteristics. The comparison of the exchange biased BLs and TLs that are studied here with the plain ones studied in D. Stamopoulos et al. [Phys. Rev. B 75, 184504 (2007)] enable us to reveal an underlying parameter that may falsify the interpretation of the transport properties of relevant FM-SC-FM TLs and FM-SC BLs investigated in the recent literature: the underlying mechanism motivating the extreme magnetoresistance peaks in the TLs relates to the suppression of superconductivity mainly due to the magnetic coupling of the two FM layers as the out-of-plane rotation of their magnetizations takes place across the coercive field where stray fields emerge in their whole surface owing to the multidomain magnetic state that they acquire. The relative inplane magnetization configuration of the outer FM layers exerts a secondary contribution on the SC interlayer. Since the exchange bias directly controls the in-plane magnetic order it also controls the out-of-plane rotation of the FMs' magnetizations so that the magnetoresistance peaks may be tuned at will.All the contradictory experimental data reported in the recent literature are fairly discussed under the light of our results; based on a specific prerequisite we propose a phenomenological strayfields mechanism that explains efficiently the evolution of magnetoresistance effect in TLs. Our experiments not only point out the need for a new theoretical treatment of FM-SC hybrids but also direct us toward the design of efficient supercurrent-switch elemental devices.

Magnetically assisted hemodialysis is a development of conventional hemodialysis and is based on the circulation of ferromagnetic nanoparticle-targeted binding substance conjugates (FN-TBS Cs) in the bloodstream of the patient and their eventual removal by means of a 'magnetic dialyzer'. Presented here is an in vitro investigation on the biocompatibility of bare Fe(3)O(4) FNs and Fe(3)O(4)-bovine serum albumin Cs with blood cells, namely red blood cells (RBCs), white blood cells (WBCs) and platelets (Plts). Atomic force microscopy (AFM) and optical microscopy (OM) enabled the examination of blood cells at the nanometer and micrometer level, respectively. The observations made on FN- and C-maturated blood samples are contrasted to those obtained on FN- and C-free reference blood samples subjected to exactly the same maturation procedure. Qualitatively, both AFM and OM revealed no changes in the overall shape of RBCs, WBCs and Plts. Incidents where bare FNs or Cs were bound onto the surface of RBCs or internalized by WBCs were very rare. Detailed examination by means of OM proved that impaired coagulation of Plts is not initiated/promoted either by FNs or Cs. Quantitatively, the statistical analysis of the obtained AFM images from RBC surfaces clearly revealed that the mean surface roughness of RBCs maturated with bare FNs or Cs was identical to the one of reference RBCs.