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An up-to-11-fold enhancement was observed in the in-magnetic-field critical current density (J c ) in epitaxial YBa 2 Cu 3 O 7 films on CeO 2 -buffered SrTiO 3 substrates by irradiation with 200-to 750-keV Si and 200-keV B ions. This enhancement indicates that ion beams in the range of 100 to 1000 keV, which are widely used for modifying the conductive properties of semiconducting materials, can significantly improve the vortex-pinning properties in second-generation superconducting wires. Also observed was a scaling relation between J c and the density of the vacancies (i.e., of Frenkel pairs) produced by the nuclear collisions between incident ions and target atoms, suggesting that this density is a key parameter in determining the magnitude of the J c enhancement. Also observed was an additional J c enhancement by a modification of the depth distribution of the vacancies, thus demonstrating the flexibility in controlling artificial pinning center (APC) properties in physical APC introduction. V C 2015 AIP Publishing LLC.

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We fabricated continuous highly (110)/(101)-oriented β-FeSi2 films on Si (111) substrates by the facing-target sputtering method. An epitaxial thin β-FeSi2 template buffer layer preformed on the silicon substrate was found to be essential in the epitaxial growth of thick β-FeSi2 films. It was proved that the template reduced the iron diffusion into the silicon substrate during thick β-FeSi2 film fabrication. Even though the annealing was performed at high temperature (880 °C) for a long duration (10 h), iron diffusion was effectively hindered by the template. By introducing this template buffer layer, an abrupt interface without appreciable defects between the β-FeSi2 film and the silicon substrate formed. The mechanism for the reduction of iron diffusion by the template buffer layer is discussed.