Tunable Magnetic Remanence of Antiferromagnetically Coupled Fe₃O₄@SiO₂ Nanoparticles for In Vivo Biomedical...

Magnetic nanoparticles with zero magnetic remanence, which can be noninvasively switched to a high magnetization state, represent a promising route for biomedical applications. Here, we report on nanoparticles consisting of ferrimagnetic Fe₃O₄ half-ellipsoids in a shell of SiO₂ whose magnetization can be noninvasively set to an antiparallel-coupled (zero stray field) or ferromagnetically coupled state (maximum stray field). The hybrid particle is enclosed by a diamagnetic SiO₂ coating protecting it against the environment and allowing functionalization for specific drug targeting. Through micromagnetic simulations, we demonstrate the feasibility to noninvasively tune the magnetic remanence of these synthetic ellipsoidal magnetic particles from zero for the antiferromagnetic-coupled state to a maximum magnetization for the ferromagnetic-coupled state. This control renders the particles remarkable for in vivo biomedical applications requiring magnetomechanical or magnetothermal activation.