Vortex dynamics differences in YBaCuO at low temperatures for H||ab planes due to twin boundary pinning anysotropy

TL;DR

This study investigates vortex dynamics and pinning anisotropy in YBaCuO superconductors at low temperatures, revealing how twin boundary orientation affects magnetization, critical current, and flux behavior.

Contribution

It provides new insights into vortex behavior and pinning anisotropy in YBaCuO at low temperatures, highlighting the impact of twin boundary orientation on vortex expulsion and flux jumps.

Findings

Vortex expulsion is easier for H||TB than HperpTB.

Critical current Jc(HperpTB) exceeds Jc(H||TB) below 12 K.

Flux jumps depend on magnetic field orientation relative to twin boundaries.

Abstract

We measured magnetization, M, of a twin-aligned single crystal of YBa2Cu 3Ox (YBaCuO), with Tc = 91 K, as a function of temperature, T, and magnetic field, H, with H applied along the ab planes. Isothermal M-vs.-H and M-vs.-time curves were obtained with H applied parallel and perpendicular to the twin boundary, TB, direction. M-vs.-H curves exhibited two minimums below 38 K, which resembled similar curves that have been obtained in YBaCuO for H parallel to c axis. Above 12 K, the field positions of the minimums for H||TB and HperpTB were quite similar. Below 12 K, the position of the second minimum, Hmin, occurred at a higher field value with H||TB. Below 6 K, only one minimum appeared for both field directions. At low temperatures, these minimums in the M-vs.-H curves produced maximums in the critical current. It was determined that vortex lines were expelled more easily for H||TB than for HperpTB, and, therefore, below a certain field value, that Jc(HperpTB) was larger than Jc(H||TB) . At T<12 K with H||TB, the relaxation rate for flux lines leaving the crystal was found to be different from that for flux entering the crystal. We also observed flux jumps at low temperatures, with their sizes depending on the orientation of magnetic field with respect to the TBs.