The high-temperature superconducting bulk magnets synthesized by the heat treatment process can trap the applied magnetic field, behave as quasi-permanent magnets. The magnetic properties follow the principle of solenoid coils rather than conventional permanent magnets. Superconductivity is elevated as the temperature decreases, so by using a refrigerator to cool the magnet below the liquid nitrogen temperature, the magnetic field intensity far exceeds that generated by permanent magnets and copper coils, which is comparable to that of superconducting solenoid magnets. Applications of bulk magnets can be classified into passive applications that utilize magnetic levitation force against an external magnetic field and active ones that trap strong magnetic fields by magnetizing them. These are unique applications available only with superconductivity. Magnetic separation and NMR magnets are given as examples of active applications. The application to magnetic separation is characterized by its strong magnetic field gradient, which effectively separate weak magnetic substances without using any filters. In actual, paramagnetic hematite was successfully separated from its suspended water using the magnetic field on the magnetic pole surface. 8kg/day of nickel sulfate powder was separated from the waste liquid of the nickel-plating process, demonstrating the practicality of resource recovery. On the other, we succeeded in detecting NMR signals for the first time in the world in a highly stable magnetic field space on the single pole surface, which experimentally demonstrated that the bulk magnets can be used for NMR analysis instruments.
Keywords: superconductor, cryocooler, magnetic separation, NMR magnet