Enhancement of critical current density by borohydride pinning in H-doped MgB₂ bulks

The present study discovers the significant enhancement of critical current density by borohydride pinning in H-doped MgB₂ bulks. Second-phase borohydrides are formed by synthesizing MgB₂ bulks ex situ in an H₂ atmosphere and in situ with H-trapped boron based on the concept of gas doping. Second phase Mg(BH₄)₂ appears in the samples ex situ sintered in an H₂ atmosphere, leading to an enhancement of critical current density at magnetic fields over 3 T. Moreover, the in situ synthesized samples from H-trapped boron also exhibit a significantly enhanced critical current density of 1.8 × 10⁴ A cm⁻² at 20 K and 3 T, due to Mg(BH₄)₂ pinning centers that are embedded in the MgB₂ grains. In contrast, the critical current density is only 9.6 × 10³ A cm⁻² at 20 K and 3 T in an un-doped MgB₂ sample.