Orientation-Dependent Thermogenesis of Assembled Magnetic Nanoparticles in the Presence of an Alternating Magnetic Field

Thanks to thermogenesis in the presence of an alternating magnetic field, magnetic nanoparticles could play a promising role in local heating in vivo. However, the flexible control of thermogenesis for the given nanomaterials remains challenging. Here, we propose that the thermogenesis of assembled magnetic nanoparticles can be controlled by orientation of the film relative to an external field. This idea arises from the principle of energy conservation that is formulated by Poynting's theorem in electromagnetics. We firstly prove that the thermogenesis of magnetic nanoparticles under an alternating magnetic field is directly related to the energy flux of the field rather than to the field's intensity. Then, alteration of the orientation can lead to different incident electromagnetic energies for the nanoparticle film, where the cross-section of the energy absorption plays a crucial role. We developed a method to directly measure the complex susceptibility of an assembled film to confirm this point. This work could be of great importance for applications based on the electromagnetic energy conversion of nanomaterials.