ErBa2Cu3Oy Films Research Articles

Dependence of critical current properties on growth temperature and doping level of nanorods in PLD-YBa2Cu3Oy films

The vortex-Bose-glass-like irreversibility lines (ILs) emerged for 2.5 and 5.0at.% Ba–Nb–O (BNO)-doped YBa2Cu3Oy films deposited by PLD using Nd:YAG-laser. The ILs strongly depended on growth temperature (Ts) in addition to the doping level of BNO. The vortex glass region was expanded with increasing Ts or doping level of BNO. Drastic change of the nanorod morphology from short and bended nanorods to long and linear nanorods with increasing Ts was clarified. Moreover, it was found that Ts-dependent ILs were quite different from our previous results in BNO-doped ErBa2Cu3Oy films.

Relationship between vortex pinning properties and microstructure in Ba–Nb–O-doped YBa2Cu3Oy and ErBa2Cu3Oy films

In-field Jcs were improved by introducing Ba–Nb–O (BNO)-nanorods in YBa2Cu3Oy (Y123) and ErBa2Cu3Oy (Er123) films. Retention of Jc against the magnetic field for the BNO-doped Er123 film was superior to that for the BNO-doped Y123 film. Sharp distribution of local critical current density originating from vortex pinning by nanorods with uniform morphology was demonstrated in the Er123 film. On the other hand, fluctuating microstructures of nanorods formed in the Y123 film prepared by the same deposition conditions. Moreover, different growth temperature dependences of nanorod morphology between the Y123 and Er123 films were clarified.

Vortex Bose glass in ErBa2Cu3Oy films with size-controlled nanorods

Anomalous changes in irreversibility lines (ILs) and critical current properties depending on growth conditions were demonstrated in ErBa2Cu3Oy films with Ba–(Nb,Er)–O nanorods. Despite the formation of nanorods in the matrix at all growth temperatures (Ts), Bose-glass-like vortex pinning was strengthened with decreasing Ts. In particular, the behavior of ILs can be understood in terms of the morphology of introduced nanorods, and Ts strongly affects the vortex states. Our present study suggests the importance of optimization of growth conditions in the production process of rare-earth-based coated conductors containing nanorods as vortex-pinning centers.

Critical current properties and microstructures in impurity-doped ErBa2Cu3Oy films

We report minute doping effects of cobalt on critical current properties and microstructures in ErBa2Cu3Oy (Er123)/SrTiO3 thin films. Although critical temperatures (Tc) for the Co0.5%-doped Er123 films decreased with substrate temperature (Ts), magnetic-field angular (θ) dependence of Jc for the films grown at lower Ts showed clear c-axis peaks. Also from a fact that defects along the c-axis direction were observed in their cross-sectional microstructures, the c-axis peaks were derived from existence of c-axis correlated vortex pinning centers. On the other hand, Tc is almost constant for the change in Ts for the Co0.1%-doped Er123 films. Remarkable c-axis peaks were not observed in Jc–θ curves and, however, Jc(H∥ab)/Jc(H∥c) was decreased compared with that of the pure Er123 films. Namely, minute doping of cobalt showed a reduction effect of electromagnetic anisotropy of the Er123 matrix within the Co-doping levels at which Tc was maintained in ∼90K.

Microstructures of BaZrO3-doped ErBa2Cu3Oy films fabricated by different BaZrO3 supply

ErBa2Cu3Oy films including BaZrO3 are deposited using three types of targets by PLD to realize the self-oriented growth of BaZrO3 nanorods. Microstructures of the obtained films are observed using a transmission electron microscope (TEM). On the basis of the cross-sectional TEM images, the growth mechanism of the BaZrO3 nanorods is discussed. When about a half of BaZrO3-monolayer is added, it is found that the BaZrO3 is not widely segregated to BaZrO3 region and no BaZrO3 region on the ErBa2Cu3Oy surface but the BaZrO3 is homogeneously distributed with approximately 10nm periods on the ErBa2Cu3Oy surface. As a result, the crystal stress due to the differences of crystal length between the ErBa2Cu3Oy and BaZrO3 are introduced for every 10nm to the films. This behavior is probably the origin of the self-oriented growth of BaZrO3 nanorods.