High-field magneto-optical imaging of superconducting critical states beyond 10 T using a paramagnetic garnet sensor

TL;DR

This paper introduces a high-field magneto-optical imaging technique using a paramagnetic garnet sensor to visualize and analyze the critical current density in superconductors up to 13 T, enabling spatially resolved studies.

Contribution

The authors develop and demonstrate a magneto-optical imaging method capable of high-field (up to 13 T) spatially resolved visualization of superconducting critical states.

Findings

Successfully imaged magnetic flux distribution in a superconductor at 12 T.

Reconstructed the spatial distribution of critical current density from magnetic field data.

Validated the field dependence of Jc against conventional magnetization measurements.

Abstract

Spatially resolved characterization of the critical current density Jc in superconductors under high magnetic fields is crucial for both fundamental understanding and practical applications. However, conventional techniques primarily provide bulk-averaged values, making it difficult to resolve local variations of Jc, especially in high magnetic fields. In this work, we develop a magneto-optical imaging (MOI) technique that enables visualization of superconducting critical states in steady magnetic fields up to 13 T. This is achieved by employing a paramagnetic Nd-garnet indicator combined with a polarizing microscope system. Using this method, we directly image the magnetic flux distribution in a bulk single crystal of an iron-based superconductor Ba(Fe1-xCox)2As2 (x = 0.075) at 12 K and 20 K across the entire sample area (approximately 1 mm). From the measured magnetic field distributions, we quantitatively reconstruct the spatial distribution of the critical current density. The extracted field dependence of Jc is in good agreement with that obtained from conventional magnetization measurements. Furthermore, we demonstrate vector mapping of current flow within the sample by converting the magnetic field distribution into local current-density distributions. Our results establish high-field MOI as a powerful approach for spatially resolved evaluation of superconducting critical states and provide a new pathway for investigating inhomogeneous current transport in superconductors under high magnetic fields.