Increase in the infield critical current density of MgB₂ thin films by high-temperature post-annealing

We propose a novel fabrication technique based on the formation of a Nb protective layer on a MgB₂ hin film and high-temperature post-annealing to increase the critical current density (Jc) of MgB₂ films under an external magnetic field. Analyses of the crystal structure and the composition of the processed MgB₂ films confirmed the suppression of the evaporation and oxidation of Mg by high-temperature annealing above 550 °C. The MgB₂ film annealed at 650 °C exhibited a Jc of 1.62 MA cm⁻² under 5 T, which is the highest reported value for MgB₂ films, wires, and bulk samples to date

Control of the glass-liquid transition temperature in YBa2Cu3O7-x films

Magnetic field dependences of the glass-liquid transition temperature (Tg) were studied in YBa2Cu3O7−x films containing various types of nanoinclusions. The vortex configuration entangled or straight and pinning strength for each vortex are crucial to the behaviors of Tg. c-axis correlated pinning centers optimize these factors and achieve the upper limit of Tg, which is determined by loss of line tension of vortices, if they are elongated through a thickness of a sample. By optimizing pinning centers, critical temperature, and a matching field, a Tg value of 77 K can be obtained in YBa2Cu3O7−x in a magnetic field as high as 27 T

Influence of substrate type on transport properties of superconducting FeSe0.5Te0.5 thin films

FeSe0.5Te0.5 thin films were grown by pulsed laser deposition on CaF2, LaAlO3 and MgO substrates and structurally and electro-magnetically characterized in order to study the influence of the substrate on their transport properties. The in-plane lattice mismatch between FeSe0.5Te0.5 bulk and the substrates shows no influence on the lattice parameters of the films, whereas the type of substrates affects the crystalline quality of the films and, therefore, the superconducting properties. The film on MgO showed an extra peak in the angular dependence of critical current density Jc({\theta}) at {\theta} = 180{\deg} (H || c), which arises from c-axis defects as confirmed by transmission electron microscopy. In contrast, no Jc({\theta}) peaks for H || c were observed in films on CaF2 and LaAlO3. Jc({\theta}) can be scaled successfully for both films without c-axis correlated defects by the anisotropic Ginzburg-Landau (AGL) approach with appropriate anisotropy ratio {\gamma}J. The scaling parameter {\gamma}J is decreasing with decreasing temperature, which is different from what we observed in FeSe0.5Te0.5 films on Fe-buffered MgO substrates.Comment: accepted for publication in SUS