High Magnetic Field Generated by Bulk MgB₂ Prepared by Spark Plasma Sintering

From the applications' point of view, the advantage of low density given by MgB₂ material must be taken into consideration, and the generation of strong magnetic flux densities using MgB₂ should be investigated. In this paper, we have studied the magnetic properties of samples processed by a fast spark plasma sintering machine that is able to produce dense and high-quality MgB₂ samples. Experiments were carried out both on small pieces of the samples and on large-sized samples performing trapped field measurements in a field-cooling process. For temperatures between 10 and 30 K, the results show a strong dependence of the magnetic behavior of the large-sized samples to the applied magnetic field sweep rate, whereas nothing particular appeared on the small samples. As the magnetic flux density produced by MgB₂ bulks is directly linked to the potential of the applications, we report on the field produced at the surface of one single MgB₂ sample of 30-mm diameter and the field produced inside a stack of two MgB₂ samples of 20-mm diameter. A generation of magnetic flux density (magnetic polarization μ₀M) up to 4.80 T at 10 K and 3.92 T at 20 K inside the stack of the two MgB₂ samples was observed under a negative supporting field of -1.47 and -1.95 T, respectively. According to these values to their very low density and to their ease of manufacturing, MgB₂ bulks are promising materials for the applications of superconductors.