Coexistence of Magnetism and Superconductivity in Iron-Based Superconductors; Applications in High Current Conductors at High Magnetic Fields

In this project, the interplay between superconductivity and magnetism in recently discovered magnetic iron-based superconductors will be explored with a view to realising lossless high current conductors for key applications in fusion confinement, magnetic resonance imaging (MRI), MAGLEV and magnetic separation at very high fields. The coexistence of ferromagnetism and superconductivity is very rare because the strong exchange field generally breaks singlet Cooper pairs.

However, remarkable magnetic Fe-based superconductors have recently been discovered where these phenomena coexist over a very wide temperature range (~20K). These type II materials allow magnetic flux to enter in the form of microscopic superconducting vortices in an applied field. Normally crystalline defects (e.g., dislocations, grain boundaries etc.) in the superconductor 'pin' vortices at low fields and prevent them moving and dissipating energy.

However, the pinning strength falls rapidly at very high magnetic fields. Magnetic superconductors are unique in that the underlying domain structure and the network of domain walls can strongly trap vortices and prevent them from moving, even at very high magnetic fields. The ways in which the magnetic order can be tuned to maximise the superconducting critical current at very high fields will be explored.

Once this is understood, thin films of these materials will be grown by pulsed laser deposition with the goal of realising high performance commercial wires that can be produced by very low-cost routes.

The initial aim of the project is to study the link between magnetism and superconductivity in EuRbFe4As4 samples provided by Argonne National Laboratories by measuring the critical supercurrent density in the crystals using Hall probe arrays fabricated in the David Bullett Nanofabrication Facility. The measurements will demonstrate the effect magnetic ordering has on superconductivity in the crystals.

This is an interdisciplinary project based in the Centre for Nanoscience and Nanotechnology (CNAN) combining materials science, device fabrication and quantum transport. State-of-the-art scanning Hall microscopy techniques will be employed to image superconducting vortices and establish how they organise under the influence of coexisting magnetic domains and domain walls.

Additionally, model calculations may be used designed to simulate experimental systems and yield key insights into the microscopic physics at play.