Two mechanisms for the formation of the ferronematic phase studied by dielectric spectroscopy

A non-chiral ferroelectric nematic compound with a 1,3-dioxane unit in the mesogenic core called 2,3′,4′,5′-tetrafluoro-[1,1′-biphenyl]-4-yl 2,6-difluoro-4-(5-propyl-1,3-dioxan-2-yl) benzoate (DIO) was studied by dielectric spectroscopy in the frequency range 0.1 Hz–10 MHz over a wide range of temperatures. The compound exhibits three nematic phases on cooling from the isotropic phase, i.e., the ordinary paraelectric nematic N; the intermediate nematic N_X and the ferroelectric N_F phase. The least frequency process is due to the dynamics of ions. The middle frequency relaxation process P₁ is like as observed in other ferronematic compounds and this mode is a continuation of the molecular flip-flop motion in the isotropic phase to the collective dynamics of dipoles which are strongly coupled with the splay fluctuations in nematic phases. In addition to this process, DIO shows an additional collective relaxation process P₂ at higher frequencies both in the N and the N_X phases. This mode originates from the polar/chiral molecules of the opposite chirality, these arise from the spontaneous symmetry breaking of achiral mesogens in the N phase. Both collective processes, P₁ and P₂, show soft mode-like characteristic behavior on cooling from the N to the N_X-N_F phase transition temperature and are shown to contribute independently to the formation of the ferronematic N_F phase.