Magnetic interactions in epitaxial films of Mn5(Ge1−xSix)3/Ge(111) : 55Mn NMR study

55Mn NMR experiments have been performed at 4.2 K on a series of Mn5(Ge1−xSix)3 epitaxial films (0⩽x⩽0.55) to investigate changes introduced by silicon when it replaces germanium in a hexagonal Mn5Ge3 crystal lattice. The Si/Ge substitution was found to reduce the magnetic moment on manganese located in the 6 g sublattice creating a new population of manganese atoms with distinctly lower magnetic moment. This effect is attributed to the modified exchange interactions due to a lattice distortion introduced by Si. Interestingly, these modified Mn sites retain the orbital moment practically unaltered. The amount of new manganese environments in the 6 g sublattice coincides with a probability of Mn having two Si neighbors as first neighbors. Mn atoms located in the 4d sublattice are not significantly affected by the Si substitution in the studied concentration range.