A comparison between dewetting properties of amorphous Ge and GeMn layers on SiO2, followed by a detailed study of magnetic and structural properties of GeMn nanocrystals (NCs), is done by means of several characterization techniques. The formation of three-dimensional Ge and GeMn NCs by solid-state dewetting process was evidenced by transmission electron microscopy. Studying the dewetting morphologies revealed a weak dependence on the Mn content. We show that the size of the dewetted NCs is proportional to the initial film thickness. SQUID measurements of GeMn NCs show the ferromagnetic behavior of Mn5Ge3 phase with Curie temperature at 300 K. Raman spectroscopy was performed for GeMn self-assembled NCs in order to investigate the effects of Mn-doping and the nature of the capping layer on the strain level. (c) 2017 Elsevier B.V. All rights reserved.