Effect of $\hbox {C}_{4}\hbox {H}_{6}\hbox {O}_{5 }$ Adding on the Critical Current Density and Lateral Levitation Force of Bulk $\hbox {MgB}_{2}$

Abstract

We fabricated malic acid $(\hbox {C}_{4}\hbox {H}_{6}\hbox {O}_{5})$-added $\hbox {MgB}_{2}$ bulks by wet mixing and “Two-step solid state reaction method”. The effects of adding malic acid on ${ T}_{\mathrm{c}}$, ${ J}_{\mathrm{c}}-{ H}$ behaviour and lateral levitation force $({ F}_{\mathrm{x}})$ features of bulk $\hbox {MgB}_{2}$ have been investigated. A systematic decrease in the critical temperature ${ T}_{\mathrm{c}}$ with increasing adding level confirms the substitution of C at the B site of $\hbox {MgB}_{2}$. While the 4 wt% sample showed the best ${ J}_{\mathrm{c}}$ of $3.7\times 10^{4}$ $\hbox {A/cm}^{2}$ at 4 T and 5 K, 15 wt% sample showed uncompetitive lower critical current density $({ J}_{\mathrm{c}})$, which ascribes the poor connectivity due to the excessive unsubstituted C distribution at grain boundaries and the presence of high MgO amount. At 24 and 28 K, the 4 and 6 wt% malic-acid-added samples exhibit a higher lateral force than pure sample. Based on the observed values of M–H, ${ J}_{\mathrm{c}}$ (H) and lateral levitation force $({ F}_{\mathrm{x}})$, it can be concluded that the 4 wt% malic-acid-added sample is the best of the studied samples.