Record high-field superconductivity in MgB2: new perspectives for magnet technology

The quest for energy-efficient high-field magnets passes through the progress made on practical superconductors. Scientists from the Department of Quantum Matter Physics (UNIGE), the Laboratory of Advanced Technology – LTA (UNIGE, HES-SO Genève), and the Laboratoire des Champs Magnétiques Intenses of Grenoble (F) have recently shed light on the mechanisms that enhance the upper critical field in the superconducting compound MgB2 by using a non-conventional synthesis route. Their discovery could unlock the potential of this affordable material for future magnet applications.

Crystal structure of MgB2. Hexagonal magnesium-atom (grey sphere) layers alternate with honeycomb boron-atom (blue sphere) layers. Carbon (violet sphere) substitutes for boron in carbon-doped samples. ©Xavier Ravinet – UNIGE

The development of high-field magnets is crucial for many domains ranging from basic-physics research (nuclear magnetic resonance, particle colliders) and medical applications (magnetic resonance imaging, hadron therapy) to energy production (fusion energy). The use of superconductors in the place of normal-metal conductors allows magnet designers to drastically reduce the energy necessary to operate a magnet and to limit its size. Indeed, superconductors are materials in which very-high electric currents can flow without dissipating energy, contrary to what occurs in normal metals. However, superconductivity ends when the superconductor is exposed to a magnetic field higher than its upper-critical field, which represents the thermodynamic limit to superconductivity. The quest for practical superconductors with a high upper critical field is thus fundamental to advance in magnet technology.

An international team of scientists, coordinated by the Group of Applied Superconductivity of the University of Geneva, has successfully employed an innovative rapid synthesis route to enhance the upper critical field in the superconducting compound MgB2. This material attracts much attention from the applied superconductivity community because of its low cost and ease of manufacture. The scientists modelled the upper-critical-field dependence on the material-synthesis parameters using a “Design of Experiments”, which demanded the preparation and characterization of more than 50 samples. This methodological approach allowed the team of researchers, led by Prof. Carmine Senatore, to achieve a new record (~35 T at 4.2 K) for the upper critical field of MgB2 bulk samples, by introducing “disorder” in their crystal structure via carbon doping. From a wider perspective, the study points out that selective and tailored structural disorder can potentially further increase the upper critical field in MgB2, with a great benefit for the superconducting magnet technology.

Prof. Carmine Senatore,
Dr. Marco Bonura,
Matera Davide,

Read the article in Scientific Reports

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