Cultivate cheap and high-quality iron-based superconductors

Superconducting materials have zero electrical resistance at low temperature, which allows them to conduct “supercurrents” without dissipation. Recently, a group of scientists led by Dr. Kazumasa Iida of Nagoya University, Japan, developed an inexpensive and scalable way to produce high-temperature superconductors using “joint engineering” techniques. grains”. The new method could help develop stronger, inexpensive, high-operating-temperature superconductors with impactful technological applications.

The key to dissipation-free conduction of currents in superconductors in the presence of a magnetic field is a property called “pinning potential”. Pinning describes how defects in the superconducting matrix vortex against the Lorentz force. Controlling the microstructure of the material allows for the careful introduction of defects into the material to form “artificial pinning centers” (APCs), which can then improve its properties. The most common approach to introducing such defects into superconductors is “ion irradiation”. However, ion irradiation is both complicated and expensive.

In their study published in Materials NPG Asia, Professor Iida and his research team have successfully developed a thin-film superconductor that has surprisingly high pinning efficiency without APC. “Crystal materials consist of different regions with different crystal orientations called ‘grains.’ When the angle between the boundaries of different grains of the material is less than their critical angle, θ_vs, we call it a “low angle grain boundary (LAGB)”. LAGBs contribute to the blocking of magnetic flux, which improves the properties of the superconductor,” says Dr. Iida.

Iron (Fe) based superconductors (FBS) are considered the next generation superconducting technology. In their study, Professor Iida and his team developed an FBS called “Potassium (K)-doped BaFe₂As₂ (Ba122)” using a technique called “molecular beam epitaxy”, in which the superconductor is grown on a substrate. “Difficulties in controlling volatile potassium have made it difficult to achieve K-doped epitaxial Ba122, but we have succeeded in growing thin films on fluoride substrates,” says Dr. Iida.

The team then characterized the FBS using transmission electron microscopy and found that the film was composed of columnar grains about 30-60 nm wide. These grains were rotated around the main crystallographic axes by angles well inside θ_vs for K-doped Ba122 and formed LAGB gratings.

The researchers then made measurements of the electrical resistivity and magnetic properties of the thin film. They observed that the thin films had a surprisingly high critical current (the maximum current in a superconductor above which it goes into a state of dissipation). The LAGB gratings also ensured high anchoring efficiency in the material. “The field properties obtained in our study are comparable to those of ion-irradiated K-doped Ba122. In addition, grain boundary engineering is a simple technique and can be extended to industrial applications,” comments the Dr Ida.

The results of this study could accelerate the development of powerful magnets using superconductors, leading to advances in magnetic resonance imaging (MRI). The widespread application of MRI is currently limited by the high investment and running cost of MRI machines due to the cooling costs of the superconductors inside. But with simple and inexpensive techniques such as grain boundary engineering for manufacturing superconductors, MRIs could become more accessible to patients, improving our quality of life.