Enhanced Magnetic Levitation and Guidance Force in MgB2 Bulks by Synthetic Engine Oil Immersion

We have used Synthetic engine oil' as a rich easily accessible carbon source and investigated the effect of engine oil on the microstructure, critical current density (J(c)), vertical levitation force (F-z) and guidance force (F-x) properties of MgB2 superconductor. The polycrystalline disk-shaped MgB2 bulk samples have been prepared using two-step solid-state reaction process. After the first heating process, MgB2 bulk samples immersed in the engine oil for different durations (30, 120, 300 and 1440 min). XRD analysis indicated the decreasing of lattice parameters of samples and confirmed C substitution in boron sites. Vertical levitation and guidance force measurements were carried out with both Field-cooling (FC) and zero-field-cooling (ZFC) regimes at different temperatures of 20, 24 and 28 K. It was found that engine oil addition slightly increases the levitation and guidance force properties. The Fz values were obtained as 11.17 and 11.58 N for pure and MgB2 sample immersed for 30 min at 20 K in ZFC regime. In addition, the MgB2 sample immersed for 300 min in engine oil showed the highest Jc value of 5.3x104 A cm(-2) at 15 K and self-field and showed the highest guidance force value of 4.14 N at 20 K. These finding suggest that synthetic engine oil is a cost-effective and promising method to improve the levitation and guidance force performance as well as the critical current density of MgB2 bulk superconductor.