Magnetic field role in solar-driven water evaporation of Fe₃O₄/polyvinyl alcohol

Magnetically responsive materials offer unique opportunities for enhancing solar steam generation (SSG) through externally induced structural reconfiguration. In this study, we investigate the influence of magnetic field strength on the photothermal behavior of Fe₃O₄/polyvinyl alcohol (PVA)-based membranes. Under a moderate magnetic field (1876 G), the membrane self-organizes into a stable three-dimensional needle-like architecture that promotes broadband solar absorption, efficient thermal localization, and a high evaporation rate of 1.3236 kg m^-2 h^-1 under 1 sun illumination with the solar efficiency of 93.30%. However, when exposed to stronger magnetic fields (≥2355.9 G), the microstructure becomes distorted and destabilized, resulting in diminished light-harvesting capability and suppressed evaporation performance. These findings highlight the delicate balance between structural enhancement and degradation in magnetic field-assisted photothermal systems and demonstrate the critical role of controlled field strength in optimizing the efficiency of SSG devices.