Flux Pinning by Columnar Defects Along a-axis in a-axis Oriented YBCO Thin Films

Strong flux pinning by columnar defects with directionally dependent morphologies in GdBCO-coated conductors irradiated with 80 MeV Xe ions

“…The directional dependence of the morphology of CDs has been reported in terms of the cross-sectional shape of CDs in a plane-view TEM image: CDs are circular in shape when the irradiation direction is parallel to the c-axis, but larger and elliptical in shape when the irradiation is parallel to the a-axis. 11,16) One model to interpret the formation of irradiation-induced defects by heavy-ion beams is the thermal spike model: the energy of electronic excitations induced in a line along the ion track is instantaneously transferred to the lattice, which contributes to the formation of irradiation defects. 11,18) Taking the anisotropy of thermal diffusivity peculiar to high-T c superconductors into account in this model, the anisotropy of the cross-sectional shape of CDs can be described as follows: a temperature spread in the bc-plane is suppressed for the formation of CDs along the a-axis, since the thermal diffusivity along the c-axis is small; therefore, more severe structural damage is caused for the incident ion along the a-axis, resulting in a larger diameter of the elliptically shaped cross section of the CDs along the a-axis.…”

“…It has been reported that CDs along the a-axis are larger and elliptical in shape, whereas CDs along the c-axis are usually circular in shape. 11,16) The orientational dependence of the shape of CDs is attributed to the anisotropy of thermal diffusivity in high-T c superconductors, which causes more severe structural damage for the formation of CDs along the a-and/or the b-axis. 11) Hence, it is possible that heavy-ion irradiation with relatively low energy forms CDs with different morphologies in a direction tilted off the c-axis.…”

Tuning critical current density properties of YBa2Cu3O y thin films under longitudinal magnetic field by using heavy-ion irradiation

“…B || ab) compared to the unirradiated film. This is because the CDs at φ i = 0 • strongly trap the flux lines along their length at B || c, but work as channels for easy flux line motion at B || ab [27,28]. However, an overall increase in J c is caused when CDs are tilted toward the transport current direction: the two films of C87 and S85 show higher J c at B || ab than not only C00 but also the unirradiated film, whereas the values of J c at B || c are lower than that of C00.…”