Effect of thickness on structural and magnetic properties of Mn5Ge3 films grown on Ge(111) by solid phase epitaxy

We report on the structural and magnetic properties of epitaxial Mn5Ge3 films grown by molecular beam epitaxy (MBE) on Ge(111) substrates with film thicknesses ranging from 5 to ~ 185 nm. It is shown that epitaxial Mn5Ge3 films with a thickness as large as 185 nm can be obtained despite a misfit of ~ 3.7% between two materials. Measurements of the in-plane lattice parameter carried out by means of reflection high-energy electron diffraction (RHEED) revealed that Mn5Ge3 films were fully relieved of strain after deposition of the first monolayer. For film thicknesses smaller than 50 nm, the easy axis of magnetization is found to lie in the hexagonal basal (001) plan, parallel to the interface and the hard axis is perpendicular to the layers. When the film thickness increases above 50 nm, magnetization measurements with magnetic field applied in-plane of the samples reveal that the easy axis of magnetization progressively turns out of the hexagonal basal (001) plan of Mn5Ge3. Even for Mn5Ge3 films with a thickness larger than 185 nm, the easy axis of magnetization never becomes perpendicular to the sample surface as being expected for bulk Mn5Ge3 materials.