Entropic Locking Stabilized Macroscopic Ferromagnetic Phase in Colloidal Chiral Liquid Crystals

Ferronematics, a class of materials capable of forming macroscopic ferromagnetic phases and offering magnetic control, were first proposed by Brochard and de Gennes over five decades ago and have recently been realized in molecular liquid crystals. However, this powerful tool remains untapped in colloidal chiral liquid crystals. Here, we report a lyotropic ferromagnetic chiral nematic liquid crystal by homogeneously dispersing anisotropic barium hexaferrite nanoplates into a cellulose nanocrystal matrix, which enables the formation of a macroscopic chiral monodomain with responsive features under weak magnetic fields (∼50 mT). We demonstrate that the nanoplates lock their surface normal to the chiral director, guiding domain alignment and coarsening while imparting a robust ferromagnetic response. This work provides a scalable platform for low-field fabrication of monodomains with applications spanning photonics, soft actuators, sensors, radiative cooling materials, and intelligent soft matter.