A new MgB₂ bulk ring fabrication technique for use in magnetic shielding or bench-top NMR systems

Abstract

<jats:title>Abstract</jats:title> <jats:p>We report a new methodology in bulk MgB<jats:sub>2</jats:sub> ring production for use in small-scale magnetic shielding or bench-top NMR systems. This process is a modified field-assisted sintering technique (mFAST) which enables direct formation of the rings without the need for machining or additives into the precursor powder. The shielding and trapped field capabilities of three mFAST MgB<jats:sub>2</jats:sub> rings were determined using zero-field- (ZFC) and field-cooled (FC) magnetic experiments. Individual bulks trap magnetic fields up to 1.24T at 20K comparable to the highest published data for a ring sample. It is anticipated that for many applications, multiple rings will be stacked to form the required experimental structure. We find for the three ring stack a trapped field of 2.04T and a maximum shielded field of 1.74T at 20K. The major factor limiting performance at low temperatures are flux jumps which cause rapid loss of the trapped field or shielding capability. Preliminary studies of magnetic field ramp rate dependence on flux jumps were conducted illustrating that even at very slow ramp rates (0.007 T/min) they remain a significant issue. Despite this concern, we conclude that mFAST represents an exciting new fabrication methodology for bulk MgB<jats:sub>2</jats:sub> rings.</jats:p>