How would you account for the following:  The third ionization enthalpy of manganese (Z = 25) is exceptionally high.

Mn (25) has electronic configuration [Ar] 4s^2 3d^5 . Electric configuration of Mn^2+ is [Ar] 4s^0 3d^5 . After losing 2 electrons , it has half filled d-orbital, which is more stable, that's why Mn^2+ has exceptionally high third ionisation energy , i.e. the energy required to remove the third electron is very high.