Marta Z. Cieplak

Effect of noble metal buffer layers on superconducting YBa2Cu3O7 thin films

Superconducting YBa2Cu3O7 thin films have been prepared by using a magnetron sputtering system in the single‐source mode. Samples deposited on [100] single‐crystal MgO with and without a Au buffer layer all show high transition temperatures (82–87 K). The use of a Au buffer layer significantly improves the superconducting properties, particularly the Meissner effect and critical current density (3.3×106 A/cm2 at T=2 K and 3.5×104 A/cm2 at T=77 K). The Au films remain metallic after high‐temperature annealing in an oxygen atmosphere. We propose to use Au buffer layers as current shunts to protect superconducting films and devices.

Superconducting Au-YBa2Cu3O7 composites

Superconducting Au‐YBa2Cu3O7 composites have been fabricated over a Au volume fraction range of 0–100%. Microstructure measurement indicates that Au and YBa2Cu3O7 form well‐separated phases. The superconducting transition temperature Tc was found unaffected by the presence of Au. The composites exhibit low normal state resistivity and much improved ductility. The results suggest that Au is an excellent metal host for making ultrafine YBa2Cu3O7 granular solids.

Unexpected effects of gold on the structure, superconductivity, and normal state of YBa2Cu3O7

Using high‐resolution x‐ray and neutron diffraction measurements, we have shown that gold can be doped into YBa2Cu3O7 (1:2:3) up to 10% per formula unit, exclusively at the Cu(1) sites. Au doping causes a larger uniaxial expansion along the c axis, accompanying an increase in the Cu(1)—O(1) bond length and a decrease in the Cu(2)—O(1) bond length. The superconducting transition temperature (Tc) is enhanced upon Au doping and the normal‐state transport properties are altered even for small levels of Au doping. The widely held belief in the inert nature of Au with regard to high Tc superconductors is therefore invalid. These findings also raise questions concerning results using single crystals grown from gold crucibles.

Superconductivity and magnetism in transition‐element‐substituted YBa2Cu3O7 compounds

Superconducting properties of YBa2Cu3O7 have been investigated by a systematic substitution of 3d transition elements for 10% of the Cu ions. Early transition elements Ti, V, and Cr affect the superconducting temperature of YBa2Cu3O7 only slightly. Local magnetic moment formation is observed in Mn, Fe, Co, and Ni substituted compounds. Tc strongly correlates with the size of the paramagnetic moments, possibly due to scattering from the magnetic sites. Zn displays a phenomenal ability to suppress Tc because of the elimination of the 3d holes. The Zn compositional dependence of Tc indicates that the superconductivity completely disappears at 13–14 at. % of Zn. It is suggested that Zn preferentially substitutes the Cu(2) sites.

Origin of Pinning Enhancement in a Ferromagnet-Superconductor Bilayer

Vortex pinning has been studied for the superconducting Nb film covering ferromagnetic Co∕Pt multilayer with perpendicular magnetic anisotropy, in which the magnetization reversal proceeds via domain-wall motion. Large enhancement of pinning in the Nb film has been observed in the final stages of the reversal process, and we demonstrate that it is caused by residual uninverted dendrite-shaped magnetic domains.

Resistive and structural properties of La1.85Sr0.15Cu1−yZnyO4 films

Single-phase c-axis aligned La1.85Sr0.15Cu1−yZnyO4 films were grown by pulsed laser deposition with Zn contents up to a value of y of 0.12. The film properties indicate the existence of defects, in addition to the Zn impurities, that are unintentionally introduced during the film growth. These defects are probably oxygen vacancies, and have a distinctly different effect on Tc from the Zn. The separation of the two effects resolves earlier ambiguities in the observed rates of Tc depression.

Enhancement of vortex pinning in superconductor/ferromagnet bilayers via angled demagnetization

We use local and global magnetometry measurements to study the influence of magnetic domain width

Tunable phase diagram and vortex pinning in a superconductor-ferromagnet bilayer

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The effect of strain on the microstructure and superconductivity of pulsed laser deposited LaSrCuO films

on the domain-induced vortex pinning in superconducting/ferromagnetic bilayers, built of a Nb film and a ferromagnetic Co/Pt multilayer with perpendicular magnetic anisotropy, with an insulating layer to eliminate the proximity effect. The quasiperiodic domain patterns with different and systematically adjustable width

Electron spin resonance studies of the temperature dependence of the ZnS visible photoluminescence

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