Comprehensive modelling of ferrofluids via dual dissipation mechanisms for multiplexed thermal activation

Abstract Ferrofluids, composed of magnetic nanoparticles (MNPs), act as magnetothermal energy transducers under alternating magnetic fields. Heat conversion occurs through two primary mechanisms: Néel relaxation and Brownian relaxation. However, establishing activation standards for each particle type remains challenging, with significant discrepancies between theoretical and experimental values. We propose that these discrepancies arise not only from the nonlinear responses of magnetic particles but also from the simultaneous occurrence of both heat generation mechanisms. To address this issue, we propose a refined equation that considers the dual dissipation of each relaxation process. This comprehensive model predicts the transduced power more accurately and helps trace the stochastic Brownian rotation inside magnetic colloidal suspensions. Furthermore, our approach theoretically proves the multiplexed activation with three (or more) channels, which cannot be verified using the conventional theory. This study offers insights into the selection of stable operations for magnetothermal energy conversion, whether in single or multiple channels.