Enhancement of critical current density in low level Al-doped MgB2

Two sets of MgB2 samples doped with up to 5 at.% of Al were prepared in different laboratories using different procedures. Decreases in the ‘a’ and ‘c’ lattice parameters were observed with Al doping, confirming Al substitution onto the Mg site. The critical temperature (Tc) remained largely unchanged with Al doping. For 1–2.5 at.% doping, at 20 K the in-field critical current densities (Jc s) were enhanced, particularly at lower fields. At 5 K, the in-field Jc was markedly improved; for example at 5 T Jc was enhanced by a factor of 20 for a doping level of 1 at.% Al. The improved Jcs correlate with increased sample resistivity, which is indicative of an increase in the upper critical field, Hc 2, through alloying.