Measurement of the magnetic field inside the holes of a drilled bulk high-Tc superconductor

TL;DR

This study uses drilled holes in a bulk YBCO superconductor to measure local magnetic properties under AC flux, revealing three penetration regimes and demonstrating a new method for bulk magnetic characterization.

Contribution

It introduces a novel technique of probing internal magnetic fields in a superconductor using miniature coils in drilled holes, providing detailed insight into flux penetration regimes.

Findings

Identified three distinct flux penetration regimes within the holes.

Demonstrated correlation between internal magnetic fields and surface flux density.

Showed the method's potential for local magnetic property characterization.

Abstract

We use macroscopic holes drilled in a bulk YBCO superconductor to probe its magnetic properties in the volume of the sample. The sample is subjected to an AC magnetic flux with a density ranging from 30mT to 130mT and the flux in the superconductor is probed by miniature coils inserted in the holes. In a given hole, three different penetration regimes can be observed: (i) the shielded regime, where no magnetic flux threads the hole; (ii) the gradual penetration regime, where the waveform of the magnetic field has a clipped sine shape whose fundamental component scales with the applied field; and (iii) the flux concentration regime, where the waveform of the magnetic field is nearly a sine wave, with an amplitude exceeding that of the applied field by up to a factor of two. The distribution of the penetration regimes in the holes is compared with that of the magnetic flux density at the top and bottom surfaces of the sample, and is interpreted with the help of optical polarized light micrographs of these surfaces. We show that the measurement of the magnetic field inside the holes can be used as a local characterization of the bulk magnetic properties of the sample.