The thickness and magnetic field dependence of resistance in Co/Nb multilayers with current perpendicular to plane geometry were measured at 4.2 K. When the number of bilayers increased, the resistance increased linearly. This linear behavior enables us to use a series resistance model to analyze our data for the thicknesses we used, 20 and 80 nm for Nb. When sandwiched between Co, Nb is a normal metal when thinner than 30 nm, otherwise it is superconducting. Assuming bulk resistivities for normal Nb and Co, we got unit area resistance values of 6.3 and 3.5 fΩ m2 for superconducting and normal Nb/Co interfaces. There was no magnetoresistance observed, at a resolution of about 0.1%. The applicability of a diffusive regime model is discussed.

We fabricated lateral junctions by crossing superconducting Nb strips in metallic contact with a ferromagnetic NiFe strip. Transport measurements on the Nb lateral junctions exhibit modulations of the critical current with a varying perpendicular magnetic field similar to a Fraunhofer interference pattern, which demonstrates the dc Josephson effect. The modulations of the critical current could be attributed to an effective weak link embedded in the Nb strip and formed a Josephson junction. Appearance of Shapiro steps on the current-voltage curves of these junctions when microwaves irradiation is applied proves the ac Josephson effect. The underlying physics of the effective weak link induced by the NiFe strip is discussed.

Spin polarized current is the main ingredient of diluted magnetic oxides due to its potential manipulation in spintronic devices. However, most research has focused on ferromagnetic properties rather than polarization of electric current, because direct measurements were difficult and the origin of spin polarized currents has yet to be fully understood. The method to increase the spin polarized current percentage is beyond practical consideration at the present status. To target this problem, we focus on the role of oxygen vacancies and nano grain size on the spin polarized current, which are controlled by growing the Co-doped ZnO thin-films at room temperature in a reducing atmosphere [Ar + (1% ~ 30%) H 2 ]. We found that the conductivity increases with an increase in oxygen vacancies via two independent channels: the variable range hopping (VRH) within localized states and the itinerant transport in the conduction band. The Andreev Reflection measurements prove that the VRH conduction is equivalent to spin polarized current. Transport measurements show that the best way to increase the VRH content, or the percentage of spin polarized current, is to increase oxygen vacancy concentration and to reduce grain size and lattice constants of the films. *Corresponding Author: hchou@mail.nsysu.edu.tw A series of Zn 0.95 Co 0.05 O 1-δ (CZO) thin-films were grown, by standard magnetron sputtering in a reducing atmosphere, on glass and fused quartz substrates. For reducing atmosphere, we used a mixture of Ar and 1% ~ 30% of H 2 (specified as #% such that CZO films grown at a specific H 2 % are written as CZO-#%). Unlike other high temperature processing conditions, these thin-films were grown at room temperature in order to reduce the possibility of hydrogen doping in films.Crystal structures and phase purity of as-grown thin-films were examined by a Bede D1 High resolution X-ray diffractometer. Near edge X-ray absorption spectroscopy (NEXAS) and extended X-ray absorption fine structure (EXAFS) were performed in Taiwan's NSRRC 01C1 beam line, on the Co K-edge.Optical transmittance spectra were recorded with an N&K analyzer 1280 (N&K technology Inc.).Conductivity measurements were performed via a conventional four probe method. The conductance-voltage (G-V) curves were measured at 4.2 K temperature by the differential technique. A three-step delta technique was used to measure the differential conductance as a function of applied voltage on the point contacts. We used a Keithley 6221 current source to provide an alternating staircase sweep current. The amplitude of the alternating portion of the current is the differential current (dI). Each delta voltage is averaged with the previous delta voltage to calculate the differential voltage (dV). The differential conductance (ΔG) can be derived using dI/dV. Each conductance curve was normalized by its high-bias value for further analysis. Results and discussion:Since Co-clusters and incorporated hydrogen in ZnO crystal lattice can disturb the spin polarized current and the ferro...

We study the spin dependent transport at the junctions between two superconducting Nb leads connected by two ferromagnetic NiFe bars in parallel, which have various separations. The separation distance l between NiFe bars was varied from 150 to 700 nm to study the spin relaxation effect in Nb. In small l (150 and 250 nm) samples, a spin-valve-like behavior related to the inverse proximity effect was observed, which manifest itself as charge accumulation due to spin imbalance near the interface. However, for samples with large l, the spin-valve behavior vanishes and the anisotropic magnetoresistance effect dominates.