Flux pinning behaviors of Ti and C co-doped MgB2 superconductors

Flux pinning behavior of carbon and titanium concurrently doped MgB2 alloys has been studied by ac susceptibility and dc magnetization measurements. It is found that critical current density and irreversibility field of MgB2 have been significantly improved by doping C and Ti concurrently, sharply contrasted to the situation of C-only-doped or Ti-only-doped MgB2 samples. AC susceptibility measurement reveals that the dependence of the pinning potential on the dc applied field of Mg0.95Ti0.05B1.95C0.05 has been determined to be U(Bdc)∝Bdc-1 compared to that of MgB2U(Bdc)∝Bdc-1.5. As to the U(J) behavior, a relationship of U(J) ∝ J−0.17 is found fitting well for Mg0.95Ti0.05B1.95C0.05 with respect to U(J) ∝ J−0.21 for MgB2. All the results reveal a strong enhancement of the high field pinning potential in C and Ti co-doped MgB2.