Formation and pinning properties of growth-controlled nanoscale precipitates in YBa₂Cu₃O7−δ/transition metal quasi-multilayers

To study the possibility of enhancing the pinning forces in YBa 2 Cu 3 O 7−δ films through the introduction of nanosized precipitates, quasi-multilayers of YBa 2 Cu 3 O 7−δ and a transition metal (TM = Ti,Zr,Hf) were deposited on single-crystal SrTiO 3 substrates using pulsed laser deposition. The transition metal layer thickness was chosen to be less than one unit cell, resulting in separated nanoscale islands that form inclusions with perovskite structure BaTM O 3 during film growth. These inclusions grow biaxially textured within the film. Whereas the Ti-doped films show a very strong decrease in the critical temperature T c and, hence, a strong decrease in the critical current density J c with increasing TM amount for all temperatures, Hf and Zr doping show an increase in J c for the smallest amounts of doping. An irreversibility field as high as 10.3 T at 77 K was observed in the case of low Hf content.