Development of High-Performance QMG Bulk Magnets for High Magnetic Field Engineering Applications

This paper describes the recent progress in QMG bulks in Nippon Steel and Sumitomo Metal Corporation. QMG is a high-J(c) bulk material, which consists of a single crystalline RE123 phase with finely dispersed RE211 particles. QMG bulks have a significant potential for high-field engineering applications, since they can trap high magnetic fields depending on their J(c) and size. Gd-QMG bulks are very attractive for various bulk applications such as flywheel energy storage systems, ship motors, wind power generators, etc. The trapped magnetic field of Gd-QMG bulks 60 mm in diameter at 77 K is twice as large as that of Y-QMG bulks with a similar size due to their excellent J(c) properties. An enlargement in the diameter of the bulk leads to the enhancement of the trapped magnetic field. The large Gd-based QMG bulks up to 150 mm in diameter were fabricated by incorporating the RE compositional gradient method. Compact nuclear magnetic resonance (NMR)/MRI spectrometers are one of the promising applications of bulk superconductors. Eu-QMG bulks are suitable for NMR magnets. NMR applications require extremely homogenous magnetic fields. In the Eu-system, the small paramagnetic moment of the Eu ion compared to the Gd ion improves the field homogeneity in the bulk.