Magnetic order in nanogranular iron germanium films

We study the effect of strain on the magnetic properties and magnetization configurations in nanogranular FexGe1−x films (x = 0.53 ±0.05) with and without B20 FeGe nanocrystals surrounded by an amorphous structure. Relaxed films on amorphous silicon nitride membranes reveal a disordered skyrmion phase while films near and on top of a rigid substrate favor ferromagnetism and an anisotropic hybridization of Fe d levels and spin-polarized Ge sp band states. The weakly coupled topological states emerge at room temperature and become more abundant at cryogenic temperatures without showing indications of pinning at defects or confinement to individual grains. Our results demonstrate the possibility to control magnetic exchange and topological magnetism by strain and that rigid wafers and free-standing membranes yield distinct physical properties due to varying deposition conditions (thermal conductance) and strain relaxation, generally preventing the inference from one batch to another.