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1. Pinning Efficiency of One-Dimensional Artificial Pinning Centers in YBa ₂ Cu ₃ O _7-x Thin Films

   https://doi.org/10.1109/TASC.2019.2895739  

   Wu, Judy; Gautam, Bibek; Sebastian, Mary Ann; Ogunjimi, Victor; Misra, Shikhar; Huang, Jijie; Baca, Javier; Prestigiacomo, Joseph; Haugan, Timothy; Wang, Haiyan; et al (August 2019, IEEE Transactions on Applied Superconductivity)
2. Polarization pinning at antiphase boundaries in multiferroic YbFeO ₃

   https://doi.org/10.1088/1674-1056/ad8cbc  

   Ren, Guodong; Omprakash, Pravan; Li, Xin; Yun, Yu; Thind, Arashdeep S; Xu, Xiaoshan; Mishra, Rohan (November 2024, Chinese Physics B)

   Abstract The switching characteristics of ferroelectrics and multiferroics are influenced by the interaction of topological defects with domain walls. We report on the pinning of polarization due to antiphase boundaries in thin films of the multiferroic hexagonal YbFeO₃. We have directly resolved the atomic structure of a sharp antiphase boundary (APB) in YbFeO₃thin films using a combination of aberration-corrected scanning transmission electron microscopy (STEM) and total energy calculations based on density-functional theory (DFT). We find the presence of a layer of FeO₆octahedra at the APB that bridges the adjacent domains. STEM imaging shows a reversal in the direction of polarization on moving across the APB, which DFT calculations confirm is structural in nature as the polarization reversal reduces the distortion of the FeO₆octahedral layer at the APB. Such APBs in hexagonal perovskites are expected to serve as domain-wall pinning sites and hinder ferroelectric switching of the domains. 

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3. The effect of APC/YBCO interface on the angular range of effective pinning by one-dimensional artificial pinning centers in YBa ₂ Cu ₃ O _7-x nanocomposite films

   https://doi.org/10.1088/1757-899X/756/1/012025  

   Ogunjimi, V; Gautam, B; Sebastian, M.A.; Haugan, T; Wu, J (March 2020, IOP Conference Series: Materials Science and Engineering)
4. Comparison Study of the Flux Pinning Enhancement of YBa ₂ Cu ₃ O _7−δ Thin Films With BaHfO ₃ + Y ₂ O ₃ Single- and Mixed-Phase Additions

   https://doi.org/10.1109/TASC.2019.2892324  

   Sebastian, Mary Ann; Gautam, Bibek; Ebbing, Charles R.; Panasyuk, George Y.; Susner, Michael A.; Huang, Jijie; Zhang, Wenrui; Wang, Haiyan; Wu, Judy Z.; Haugan, Timothy J. (August 2019, IEEE Transactions on Applied Superconductivity)
5. Ca-repaired BaZrO ₃ nanorods/YBa ₂ Cu ₃ O _7-x interface for enhanced pinning in YBa ₂ Cu ₃ O _7-x nanocomposites with 2-8% BaZrO ₃ doping

   https://doi.org/10.1088/1757-899X/1302/1/012013  

   Wu, Judy; Panth, Mohan; Ogunjimi, Victor; Ann_Sebastian, Mary; Zhang, Di; Haugan, Timothy; Wang, Haiyan (May 2024, IOP Conference Series: Materials Science and Engineering)

   Abstract C-axis aligned BaZrO₃(BZO) nanorods formed via strain-mediated self-assembly in BZO-doped YaBa₂Cu₃O_7-x(BZO/YBCO) nanocomposite films can provide strong pinning to the quantized magnetic vortices. While the strain initiated from the BZO/YBCO lattice mismatch plays a critical role in nucleation and evolution of the BZO nanorods, it also leads to a highly defective BZO/YBCO interface and hence reduced pinning efficiency of BZO nanorods. This work reports a recent study in probing the effect of BZO/YBCO interface on the pinning efficiency of the BZO nanorods as the interface is repaired dynamically during the BZO nanorod growth using Ca doping. Within the BZO doping range of 2-8 vol.%, significantly enhanced pinning efficiency of the BZO nanorods have been observed. A peak enhancement up to five-fold of critical current density at 9.0 T and 65-77 K has been obtained in the 6 vol.% BZO/YBCO nanocomposites after the interface repair. This result not only illustrates the critical importance of the BZO/YBCO interface in the pinning efficiency, but also provides a facile scheme to achieve such an interface to restore the pristine pinning efficiency of the BZO nanorods. 

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