We report on the Mn segregation and diffusion during the epitaxial overgrowth of Ge on Mn 5Ge 3/Ge(111) heterostructures. It is shown that the underneath Mn 5Ge 3 layers remain stabilized at the interface with the substrate while a small amount of Mn can leave the layers and floats at the Ge growth front. Mn can then act as a surfactant during Ge growth along the (111) orientation. The Mn segregation length and also the state of Mn atoms incorporated in the Ge layers are found to depend on the growth temperature. At a growth temperature of 250 °C, a segregation length of ~ 10 nm is observed and Mn atoms incorporated in the Ge layers are uniformly distributed. At 450 °C, segregated Mn atoms can react with Ge to form Mn 5Ge 3 clusters inside the Ge overgrown layer. Such Mn 5Ge 3 clusters display random orientations and induce modification of the magnetic anisotropy of the whole film.