Transformational dynamics of BZO and BHO nanorods imposed by Y 2 O 3 nanoparticles for improved isotropic pinning in YBa 2 Cu 3 O 7−δ thin films

Bibek Gautam, Mary Ann Sebastian, Shihong Chen, Jack Shi, Timothy
Haugan, Zhongwen Xing, Wenrui Zhang, Jijie Huang, Haiyan Wang, Mike
Osofsky, Joseph Prestigiacomo, and Judy Z. Wu
AIP Advances 7, 075308 (2017); doi: http://dx.doi.org/10.1063/1.4991051

An elastic strain model was applied to evaluate the rigidity of the c-axis aligned
one-dimensional artificial pinning centers (1D-APCs) in YBa 2 Cu 3 O 7-δ matrix films. Higher
rigidity was predicted for BaZrO 3 1D-APCs than that of the BaHfO 3 1D-APCs. This
suggests a secondary APC doping of Y 2 O 3 in the 1D-APC/YBa 2 Cu 3 O 7-δ nanocomposite films
would generate a stronger perturbation to the c-axis alignment of the BaHfO 3 1D-APCs
and therefore a more isotropic magnetic vortex pinning landscape. In order to
experimentally confirm this, we have made a comparative study of the critical current
density J c (H, θ, T) of 2 vol.% BaZrO 3 + 3 vol.%Y 2 O 3 and 2 vol.%BaHfO 3 + 3 vol.%Y 2 O 3
double-doped (DD) YBa 2 Cu 3 O 7-δ films deposited at their optimal growth conditions. A
much enhanced isotropic pinning was observed in the BaHfO 3 DD samples. For example,
at 65 K and 9.0 T, the variation of the J c across the entire θ range from θ=0 (H//c) to
θ=90 degree (H//ab) is less than 18% for BaHfO 3 DD films, in contrast to about 100% for
the BaZrO 3 DD counterpart. In addition, lower α values from the J c (H) ∼ H -α fitting were
observed in the BaHfO 3 DD films in a large θ range away from the H//c-axis. Since the
two samples have comparable J c values at H//c-axis, the improved isotropic pinning in
BaHfO 3 DD films confirms the theoretically predicted higher tunability of the BaHfO 3 1D-
APCs in APC/YBa 2 Cu 3 O 7-δ nanocomposite films.