Effect of combined addition of graphene oxide and citric acid on superconducting properties of MgB2

•We synthesized all the samples using standard solid state reaction method.•Graphene oxide (GO) and citric acid are added in MgB2.•Hc2(0) is calculated from two-band GL-theory fit.•JC(H) is improved with increased grain connectivity and flux pinning.•Behavior of flux-pinning is studied.

In the present work, polycrystalline samples with compositions MgB2 + 3wt% GO + x wt% C6H8O7 (x = 0, 5 and 10) have been synthesized to study the effect of combined addition of graphene oxide (GO) and citric acid (C6H8O7) on superconducting properties of MgB2. X-ray diffraction studies show the formation of hexagonal crystal structure of MgB2 with space group P6/mmm in all synthesized samples. We observe that the addition of GO in the sample improves the grain connectivity and consequently enhances the critical current density significantly with no substantial change in Tc. However for this sample, there is no significant improvement in Hc2 and Hirr. With the combined addition of GO and citric acid, the JC(H), Hc2 and Hirr are observed to improve substantially as compared to the pristine MgB2 and GO added MgB2 samples. For example JC(10 K, 5 T) of sample x = 10 has improved by a factor of ∼15 as compared to pure MgB2 sample and by a factor of ∼5.5 as compared to the x = 0 sample. Furthermore, Hc2(0) for x = 10 sample has enhanced by 13 T as compared to pure MgB2 while it has increased by ∼10 T in comparison to x = 0 sample. Enhanced flux pinning has been observed with the combined addition of GO and citric acid.