Quasistatic reorientation of ferromagnetic nematic colloids in a slowly rotating magnetic field

We report the development of ferromagnetic nematic colloids using a two-step protocol tailored for investigating emergent magnetoelastic phenomena. First, we prepared a ferromagnetic nematic liquid crystal by dispersing well-defined magnetic nanoparticles into a conventional nematic host, ensuring magnetic ordering while preserving the characteristic director field. Subsequently, microparticles were suspended within this ferromagnetic nematic matrix that generates elastic dipoles and quadrupoles in the director field. We show that a slowly rotating magnetic field induces surface domain $\ensuremath{\pi}$ walls that quasistatically reorient the defects and linear colloidal assemblies---an effect that is absent in ordinary nematic liquid crystals lacking spontaneous magnetization. The results are interpreted using the Landau--de Gennes Q-tensor model, extended to capture the coupling between nematic and magnetic characteristics of ferromagnetic nematic liquid crystals. This composite system enables the exploration of novel elastic and magneto-optic interactions at the interface of liquid crystalline order and nanoscale magnetism, broadening the experimental landscape for both fundamental studies and potential applications in adaptive materials that involve colloidal composites.