Anisotropy Of The Irreversibility Field For Zr-Doped (Y,Gd)Ba2cu3o7-X Thin Films Up To 45 T

The anisotropic irreversibility field B-Irr of two YBa2Cu3O7-x thin films doped with additional rare earth (RE)= (Gd, Y) and Zr and containing strong correlated pins (splayed BaZrO3 nanorods and RE2O3 nanoprecipitates) has been measured over a very broad range up to 45 T at temperatures 56 K < T < T-c. We found that the experimental angular dependence of BIrr (theta) does not follow the mass anisotropy scaling BIrr (theta) = B-Irr (0)(cos(2)theta + gamma(-2) sin(2)theta)(-1/2), where gamma = (m(c)/m(ab))(1/2) = 5-6 for the RE-doped YBa2Cu3O7-x (REBCO) crystals, m(ab) and m(c) are the effective masses along the ab plane and the c-axis, respectively, and. is the angle between B and the c-axis. For B parallel to the ab planes and to the c-axis correlated pinning strongly enhances B-Irr, while at intermediate angles, B-Irr (theta) follows the scaling behavior B-Irr(theta) proportional to (cos(2)theta + gamma(-2)(RP) sin(2)theta)(-1/2) with the effective anisotropy factor gamma(RP) approximate to 3 significantly smaller than the mass anisotropy would suggest. In spite of the strong effects of c-axis BaZrO3 nanorods, we found even greater enhancements of B-Irr for fields along the ab planes than for fields parallel to the c-axis, as well as different temperature dependences of the correlated pinning contributions to B-Irr for B//ab and B//c. Our results show that the dense and strong pins, which can now be incorporated into REBCO thin films in a controlled way, exert major and diverse effects on the measured vortex pinning anisotropy and the irreversibility field over wide ranges of B and T. In particular, we show that the relative contribution of correlated pinning to B-Irr for B//c increases as the temperature increases due to the suppression of thermal fluctuations of vortices by splayed distribution of BaZrO3 nanorods.