Modeling and experimental analysis of the hysteresis losses of magnetic nanodisks for hyperthermia applications

Recently, magnetic nanostructures (MNs) obtained a lot of interest in cancer treatment, for both hyperthermia based therapies and induced cell apoptosis with cell membrane mechanical stimulation1. Focusing on hyperthermia applications, when an external ac magnetic field is applied to an ensemble of MNs dispersed in a tissue, different physical phenomena can concur to the heat generation, e.g. Néel relaxation, Brownian relaxation, hysteresis and eddy current losses. The relative contribution strongly depends on the size and physical properties of the used MNs1,2. Here, we present a micromagnetic modeling analysis and a comparison to experimental data, focusing on Ni80Fe20 nanodisks prepared via self-assembling of polystyrene nanospheres3, for possible application in magnetically mediated hyperthermia. A parametric analysis is performed by varying disk diameter (100-700 nm) and thickness (15-30 nm), to optimize the specific heating capabilities of the MNs. We focus on hysteresis losses, being the predominant heating contribution for such nanosystems. Hysteresis loops for nanodisks both arranged in 2D arrays (before detachment from the substrate) and free-standing (dispersed in a liquid) are calculated with a GPU-parallelized micromagnetic code4. The influence of interdot magnetostatic interactions and relative orientation with the applied field is analyzed. 1) X. L. Liu et al., Adv. Mater. 27, 1939–1944 (2015). 2) A. E. Deatsch and B. A. Evans, J. Magn. Magn. Mater. 354, 163–172 (2014). 3) P. Tiberto et al., J. Appl. Phys. 117, (2015). 4) O. Bottauscio and A. Manzin, J. Appl. Phys. 115, 17D122 (2014).