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.

No abstract

We have studied the phase diagram of La 1Ϫx Ca x MnO 3 for 0.5рxр0.9 using neutron powder diffraction and magnetization measurements. At 300 K all samples are paramagnetic and single phase with crystallographic symmetry Pnma. As the temperature is reduced a structural transition is observed which is to a charge-ordered state only for certain x. On further cooling the material passes to an antiferromagnetic ground state with Néel temperature T N that depends on x. For 0.8рxр0.9 the structural transformation occurs at the same temperature as the magnetic transition. Overall, the neutron-diffraction patterns were explained by considering four phase boundaries for which La 1Ϫx Ca x MnO 3 forms a distinct phase: the charge-ordered phases at xϭ0.5 and x ϭ2/3, the monoclinic and C-type magnetic structure at xϭ0. 80-0.85, and the G-type magnetic structure at xϭ1. Between these phase boundaries the magnetic reflections suggest the existence of mixed compounds containing both phases of the adjacent phase boundaries.

We have studied the phase diagram of the MgB(2) superconductor using a single crystal for the H parallel c-axis. For the first time we report the existence of peak effect in the screening current in the MgB(2) for the H parallel c-axis. In the magnetic field regime 10

We report on combined resistance and magnetic measurements in a hybrid structure (HS) of randomly distributed anisotropic CoPt magnetic nanoparticles (MN) embedded in a 160 nm Nb thick film. Our resistance measurements exhibited a sharp increase at the magnetically determined bulk upper-critical fields Hc2(T ). Above these points the resistance curves are rounded, attaining the normal state value at much higher fields identified as the surface superconductivity fields Hc3(T ). When plotted in reduced temperature units, the characteristic field lines Hc3(T ) of the HS and of a pure Nb film, prepared at exactly the same conditions, coincide for H < 10 kOe, while for fields H > 10 kOe they strongly segregate. Interestingly, the characteristic value H = 10 kOe is equal to the saturation field H MN sat of the MN. The behavior mentioned above is observed only for the case where the field is normal to the film's surface, while is absent when the field is parallel to the film. Our experimental results suggest that the observed enhancement of surface superconductivity field Hc3(T ) is possibly due to the not uniform local reduction of the external magnetic field by the dipolar fields of the MN.