Ferronematic Phase Research Articles

Threshold magnetic fields and Fréedericksz transition in a ferronematic

Continuum theory is used to analyze the effect of an applied magnetic field on a ferronematic (i.e. dilute suspension of needle-like magnetic particles in nematic liquid crystal) with soft homeotropic anchoring between the ferroparticles and the director, and positive diamagnetic anisotropy of the liquid-crystalline matrix. It is shown that in infinite ferronematic a peculiar Fréedericksz-like transition takes place, at which by a threshold way the conditions of coupling on magnetic particles vary from homeotropic anchoring to planar one. The Fréedericksz transition field and saturation field are found as a functions of material parameters of a suspension. The continuum theory predicts the existence of three ferronematic phase (homeotropic, angular, and planar) with different relative orientations of the director and magnetization. The orientational structure of these ferronematic phases is studied.

Landau description of ferrofluid to ferronematic phase transition

Landau description of ferrofluid to ferronematic phase transition

Magnetic properties of ferrocholesterics with soft particle anchoring

The influence of the external magnetic field on the orientational structure and magnetic properties of the ferrocholesteric is analyzed. A soft homeotropic coupling between the magnetic particles and the cholesteric molecules is assumed. The diamagnetic anisotropy of the matrix is chosen to be positive. In this case, the dipolar and quadrupolar mechanisms of orientational interaction with the external field compete with each other. The field being applied normal to the helix. Using the continuum theory, the occurrence of magnetic-field-induced ferrocholesteric–ferronematic transition is studied. The transition field as a function of the material parameters of a ferrocholesteric is found. It is shown that rising the field strength in the ferronematic phase leads to a change in the coupling between the particles and the director from homeotropic to planar one. A study on the structure of the domain walls in ferronematic phase is undertaken.

Structure of the Domain Walls in Soft Ferrocholesterics

Using the continuum theory the influence of the external magnetic field on the ferrocholesteric — ferronematic phase transition is analyzed. The field being applied normal to the helix. Soft homeotropic coupling between the magnetic particles and the cholesteric molecules is assumed. The diamagnetic anisotropy of the matrix is chosen to be positive. In this case the dipolar and quadrupolar mechanisms of orientational interaction with the external field compete with each other. The transition field as a function of the material parameters of a ferrocholesteric is found. The reentrant ferrocholesteric and ferronematic phases are discussed. It is shown that rising the field strength in the ferronematic phase leads to the change in the coupling between the particles and the director from homeotropic to planar one. A study on the structure of the domain walls in ferronematic phase is undertaken.

Ferrocholesteric-ferronematic transition in an external magnetic field

The influence of an external magnetic field on the orientational structure and magnetic properties of a ferrocholesteric (i.e. a magnetic suspension with a cholesteric liquid crystal as a carrier) is studied. Two mechanisms of the field influence on the ferrocholesteric are taken into account: the dipolar one due to the interaction between the field and the magnetic moments of the needle-like particles, and the quadrupolar one due to the diamagnetic susceptibility anisotropy of the cholesteric matrix. It is shown that a magnetic field applied normal to the ferrocholesteric helical axis leads to an untwisting of the spiral structure, and the ferrocholesteric undergoes a transition to ferronematic phase. The dependence of the ferrocholesteric-ferronematic transition critical field on the material parameters of a suspension is found. It is shown that the value of the critical field is strongly reduced if a dipolar regime of spiral untwisting is realized.