Continuous production of magnetic iron oxide nanocrystals by oxidative precipitation

•Industrial-scale preparation of low-cost magnetite nanoparticles.•Transfer of laboratory synthesis to a continuous-flow process.•Method based on oxidative precipitation of Fe2+ controlled by OH− excess.•Nanoparticles’ dimensions range from 40 to 300 nm.•Improved magnetic hyperthermia efficiency validated for developed nanoparticles.