Rare earth doping effects on superconducting properties of MgB2: A review

Rare earth (RE) elements and their compounds have been doped into MgB2 since the discovery of the superconductivity of MgB2. The doping effects of RE elements and RE compounds are summarized in terms of different doping methods and the accompanying variations in the superconducting transition temperature, upper critical field, irreversibility field, and critical current density (Jc). Conclusions are drawn on the doping mechanisms to demonstrate the possibility of improvement of Jc in the future. REBy phase inclusions are observed in MgB2 as nano-pinning centers with significant enhancement of Jc in MgB2 doped with Y, La, Dy, Ho, Nd, etc. Furthermore, some REs with larger magnetic moments will provide more efficient flux pinning centers with larger pinning forces, which is different with the doping effects and mechanism of ferromagnetic transition metals in MgB2. The co-doping effects of RE with other dopants are also reviewed due to the multiple advantages of different doping mechanisms.