Exploring Fe₃S₄ and Fe₃O₄ Nanoparticle-Based Magnetorheological Fluids for Superior Stability and Performance

Greigite (Fe₃S₄), a ferrimagnetic sulfide mineral with a spinel structure analogous to Fe₃O₄, was employed in magnetorheological (MR) fluids. Fe₃S₄ nanoparticles were synthesized via a solution process, with magnetic properties verified through vibrating sample magnetometry (VSM). The MR performance and suspension stability were assessed using a rotational rheometer and Turbiscan, and the results were compared to those of Fe₃O₄-based suspensions. When dispersed in silicone oil, the Fe₃S₄ suspension demonstrated MR performance that matched or surpassed that of Fe₃O₄-based suspensions. Despite the significant density mismatch between the particles and the liquid medium, the rough surface morphology of Fe₃S₄ nanoparticles enhances suspension stability by increasing interparticle friction and reducing sedimentation rates. Furthermore, Fe₃S₄'s natural abundance and low production cost provide economic advantages for MR fluid manufacturing, while its nontoxic nature makes it particularly suitable for biomedical applications.