Effect of mixed pinning landscapes produced by 6 MeV Oxygen irradiation on the resulting critical current densities J$_c$ in 1.3 $\mu$m thick GdBa$_2$Cu$_3$O$_{7-d}$ coated conductors grown by co-evaporation

Abstract

We report the influence of crystalline defects introduced by 6 MeV $^{16}$O$^{3+}$ irradiation on the critical current densities J$_c$ and flux creep rates in 1.3 $\mu$m thick GdBa$_2$Cu$_3$O$_{7-d}$ coated conductor produced by co-evaporation. Pristine films with pinning produced mainly by random nanoparticles with diameter close to 50 nm were irradiated with doses between 2x10$^{13}$ cm$^{-2}$ and 4x10$^{14}$ cm$^{-2}$. At temperatures below 40 K with the magnetic field applied parallel (H//c) and at 45{\deg} (H//45{\deg}) to the c-axis, the in-field J$_c$ dependences can be significantly improved by irradiation. For doses of 1x10$^{14}$ cm$^{-2}$ the J$_c$ values at $\mu$$_0$H = 5 T are doubled without affecting significantly the J$_c$ at small fields. Analyzing the flux creep rates as function of the temperature in both magnetic field configurations, it can be observed that the irradiation suppresses the peak associated with double-kink relaxation and increases the flux creep rates at intermediate and high temperatures. Under 0.5 T, the flux relaxation for H//c and H//45{\deg} in pristine films presents characteristic glassy exponents $\mu$ = 1.63 and $\mu$ = 1.45, respectively. For samples irradiated with 1x10$^{14}$ cm$^{-2}$, these values drop to $\mu$ = 1.45 and $\mu$ =1.24, respectively.