The rapidly growing applications of nanomagnets in magnetic drug delivery and separation in clinical diagnostics require strong and reliable magnetic vehicles. Strength conveys rapid processing, high delivery/targeting yield and rapid results when used in clinics. Reliability enables recycling of nanomagnets, regulatory-conforming drug formulations and efficient use of (expensive) antibodies in diagnostics, combined with reduced leaching (reagent loss). The present work illustrates how metal-based nanomagnets provide a two-three-times stronger magnetic particle than conventional magnetite-based materials. Ligands, antibodies or drugs can be anchored to such carbon/metal core/shell nanomagnets over covalent, hydrolysis-resistant carbon-carbon bonds. This linker chemistry resists strong acids, sterilization and prolonged storage or aggressive treatment. As dispersions, functional nanomagnets rapidly scan liquids/tissue by Brownian diffusion, capture/deliver/react at a target and are efficiently recollected after use. Metal iron-based, carbon-coated nanomagnets consist of particularly well-accepted materials and now open stable nanomagnets to a broad range of fascinating separation problems in biomedical research.