Effect of combined addition of nano-SiC and nano-Ho2O3 on the in-field critical current density of MgB2 superconductor

MgB2 superconducting samples added with nano-Ho2O3 (n-Ho2O3) and/or nano-SiC (n-SiC) have been prepared by an in situ solid state reaction method to investigate and compare the combined and individual effects of n-SiC and n-Ho2O3 on a crystal structure, critical temperature (T-C), and critical current density (J(C)) of MgB2. All the doped samples exhibit significantly enhanced in-field J(C) and the codoped sample with 2.5 wt % n-Ho2O3 and 5 wt % n-SiC gives the best performance in in-field J(C), and the enhancement is around 100 times and 2 times greater than the undoped and monodoped n-SiC samples, respectively, at 5 K and 8 T. For the n-SiC added sample, lattice distortions due to C substitution on the B site and the formation of reacted phase Mg2Si as flux pinners cause enhanced J(C) up to the maximum field studied (8 T). While in the n-Ho2O3 added sample, a reacted phase HoB4 having a strong magnetic moment forms, without any substitution at the Mg or B site, which acts as a flux pinner in order to enhance the in-field J(C). Accordingly the best codoped sample exhibits these combined benefits of n-SiC and n-Ho2O3 in MgB2 superconductor.