Development of a superconducting magnet for nuclear magnetic resonance using bulk high-temperature superconducting materials

We developed a trapped-field magnet system using a bulk high-temperature superconducting (HTS) material (Sm-Ba-Cu-O; abbreviated as Sm123) and used it to observe a signal of ¹H nuclear magnetic resonance (NMR). The compact magnet system can fit on a table and needs no conventional refrigerant such as liquid helium. The magnet has a c-axis-oriented single-domain Sm123 bulk superconductor containing 20 wt.% Ag and was synthesized in the melt-textured process. The magnet is constructed of two cylindrical pieces, 36-mm outer and 7-mm inner diameters, respectively, and 16-mm thickness. This configuration results in magnetic field stability and suitable homogeneity for observation of NMR signal. The magnet was magnetized to 3 T by an ordinary NMR superconducting magnet by using a field cooling (FC) method. The bulk magnet was magnetized at 60K and has been kept at the temperature under 58K by using a pulse tube refrigerator. We observed ¹H NMR signal from the silicon rubber with the size of 1.2 mm diameter and 1.5 mm length at 2.89 Tesla (123 MHz) and 228 kHz peak width.