Some of the best controlled nanomotors are magnetic . A challenge is to find magnetic materials with strong magnetic moments and high remanence and coercivity, that are also biocompatible and stable against physical agglomeration at high densities. Progress in this direction has been made with the biocompatible hard magnetic FePt system , and with ZnFe coating , which protects against physical agglomeration while allowing magnetic hyperthermia. Including Mg and Zn in the scaffold of the nanomotors allows the degradation to be tuned . Ideally, one should employ hard magnetic materials that are also biodegradable.