Temperature dependence of the critical magnetic field of the structural transition in MBBA-based ferronematics

Abstract

We studied the structural transitions in ferronematics based on the thermotropic nematic liquid crystal MBBA (4^′ -methoxybenzylidene-4-n-butylaniline) having a nematic-to-isotropic transition temperature T _N–I = 48.0^○C and in MBBA-based ferronematics doped with a magnetic suspension consisting of Fe₃O₄ particles (10 nm in diameter) coated with oleic acid as a surfactant. The ferronematic samples were prepared with different volume concentrations of magnetic particles φ =,1× 10⁻⁴, 2× 10⁻⁴ and 5×10⁻⁴. The temperature dependences of the critical magnetic fields in a bias electric field under strong applied magnetic fields are presented. We calculated the surface density of anchoring energy W at the nematic–magnetic particle boundary. Scaling of the structural transition in the MBBA and MBBA-based ferronematics with the temperature of the nematic-to-isotropic transition was observed.

Keywords:

• Fine magnetic particles
• Liquid crystal
• Anchoring energy

Acknowledgements

This work was supported by the Grant Agency VEGA under grant No. 6166 and by the Science and Technology Assistance Agency APVT under contract No. 51-027904.