Mn substitution effect on superconducting properties of MgB2 single crystals

We have prepared Mn substituted MgB2 single crystals and measured their physical properties. The transition temperature (T c) steeply decreased with increasing Mn content. In the Raman spectrum, the E 2g-phonon frequency hardly shifted from that of parent MgB2, in sharp contrast to the case of Al/C substitution. This implies that the mechanisms of T c suppression are different between Al/C substitution and Mn substitution