High magnetic field enhancement of the critical current density by Ge, GeO2 and Ge2C6H10O7 additions to MgB2

Ge, GeO 2 and Ge 2 C 6 H 10 O 7 additions to MgB 2 obtained by ex situ spark plasma sintering significantly enhance the critical current density J c in high magnetic fields. A J c ( T  = 20 K) of 10 2  A cm −2 is obtained at 3.9 T in the pristine sample and at 5.8 T in the MgB 2 (Ge 2 C 6 H 10 O 7 ) 0.0014 sample. The decrease in the critical temperature for added samples is less than 1 K and J c (20 K, H  = 0) shows a small decrease from 5.5 × 10 5  A cm −2 in the pristine sample to 3.9 × 10 5  A cm −2 in MgB 2 (Ge 2 C 6 H 10 O 7 ) 0.0014 sample. Ge does not substitute into the MgB 2 lattice.