Tuning the Rate-Dependent Stiffness of Materials by Exploiting Néel Relaxation of Magnetic Nanoparticles


  • This research was supported by the U.S. Army through the Institute for Soldier Nanotechnologies, under Contract DAAD-19-02-D0002 with the U.S. Army Research Office. The authors also thank Suraj Deshmukh for assistance with the drop ball test.


The effective stiffness of materials that are impregnated with magnetic nanoparticles can be modulated by magnetic fields if the nanoparticle Néel relaxation rates are slower than the characteristic deformation rates. A numerical analysis indicates that the deflection of magnetic dipoles against the applied magnetic field on deformation of the material provides the energy absorption necessary for the enhanced stiffness observed in drop ball impact tests. The penetration depth, fraction of the impact energy that is absorbed by the rotating dipoles, and the effective increase in stiffness are shown to depend uniquely on the ratio of the characteristic magnetic energy density relative to the elastic energy density, and on the shape of the impacting object.