Prof. Martin Čopič: Ferromagnetic Liquid Crystals

43 years ago Pierre de Gennes hypothesized that a suspension of magnetic particles in nematic liquid crystal can have ferromagnetic properties. Experiments with elongated particles were unsuccessful as either the particles aggregated or the system remained paramagnetic. Nanosized platelets of barium hexaferrite, recently synthesized by Darja Lesjak and Miha Drofenik, order due to elastic forces mediated by the liquid crystal in such a way that magnetic dipolar interaction causes the suspension to become ferromagnetic. Characteristic magnetizing curve is observed, and domains can be switched by external magnetic field. The system shows strong optical response to small magnetic fields. The relaxation rate of the nematic fluctuations, which are coupled to the magnetization, depends linearly on the applied field. The system is well described by a simple free energy*.   

* A. Mertelj, D. Lisjak, M. Drofenik & M. Čopič, Nature, 504, 237 (2013).