Investigation on superconducting and magnetic levitation force behaviour of excess Mg doped-bulk MgB2 superconductors

A series bulk samples of MgB2 + x wt% of Mg (x = 0, 5, 10, 15, 20 and 30) were fabricated by solid state reaction method. The structural and electromagnetic properties of MgB2 samples were studied using X-ray diffraction (XRD), scanning electronic microscope (SEM), electrical resistivity (R-T), magnetic hysteresis (M-H), magnetic levitation (F-z) force and lateral force (F-x) measurements. The maximum repulsive and attractive force values of 15 wt% of excess magnesium MgB2 sample compared to the other samples imply that the intergranular connection between grains enhanced while pore and microcrack density decreased which brings an increase in the values of the radius of a shielding current loop (r) and the critical current density (J(c)). It was determined that to obtain the enhancement of the micro and macro structure properties, causing to the higher critical current density, and the maximum levitation and lateral force values, the optimum excess magnesium content was 15 wt % into sample. It is thought that an addition of 10-15% excess magnesium can be tried for spark plasma or other methods -as a further research- and the results showed a potential to guide the researchers to study on the material-fabrication and the magnetic bearing system.