Abstract: The invention relates to a method for producing sub-micrometric particles, which comprises: mechanochemical treatment of homogeneous or heterogeneous magnetic materials until a mass which consists mostly of magnetic nanocrystal aggregates is obtained; selection of aggregates so that the nanocrystals have a Curie temperature within a predefined variation range; functionalization of the aggregates in order to obtain coating thereof with molecules of one or more of the following types of substances: substances for which the tumour cells have a particular metabolic avidity; substances having a biochemical affinity with the tumour cells; substances having an affinity with the acid microenvironment which surrounds the neoplastic cells.