Color imaging the magnetic field distribution in superconductors

Abstract

Quantitative imaging of stray fields and magnetization distributions in hard magnetic element arraysA magneto-optically active glass was used to image the magnetic field distribution in superconductors using the Faraday effect. Polarized white light illumination of the glass resulted in. various colors depending on the setting of the analyzing polaroid. These colors are shown to be consistent with the known dependence of the Faraday rotation angle on the applied magnetic field, the temperature of the glass, and the wavelength of the light. This technique was used to observe field distributions in poly crystalline and single-crystal YBa Z Cu 3 0 7 samples. In the ceramic sample, the field was uniform within the resolution (50 Itm) of this technique and field magnitudes were measured with a 10% accuracy. In the single crystal, the magnetic field distribution was not uniform showing field gradients imaged as color gradients on the pictures of the glass. Contours of constant magnetic field were drawn from these photographs and from these, a critical current density of 10 9 A/m 2 was deduced in an external field of 136 mT.

Quantitative analysis of current density distributions from magneto-optical images of superconducting YBa2Cu3O7 thin films

“…Magneto-optical imaging (MOI) is a useful tool for imaging the magnetic field associated properties of various materials [1,2]. MOI has been applied to superconducting samples in small fields, providing visual information about the magnetic flux distribution, flux dynamics in bulk conductors [3,4], flux penetration into irradiated conductors [5], and flux penetration within filaments of powder in tube conductors [6] and along networks of grain boundaries in thin film superconducting tapes, deposited on crystalline substrates with various composite layers (coated conductors) [7][8][9][10][11][12][13][14][15][16][17]. The MOI technique has also been employed to experimentally determine current densities of various conductors by determining a field distribution from a current density theory (Biot-Savart) or from an inverted Biot-Savart calculation to determine the current densities directly [18,19].…”

Magnetic field penetration into YBa2Cu3O7 thin film deposited on a cleaved MgO substrate

“…Magnetic field penetration into the superconducting film was monitored using a magneto-optic apparatus described in more detail in a previous paper (6). A magneto-optically active glass containing terbium, 2.54 cm in diameter and 1 mm thick, was placed in direct contact with the superconducting film.…”