Magnetic instabilities of smectic C liquid crystals studied by electron spin resonance spectroscopy

Abstract

Single crystals of smectic C samples in a magnetic field will deform so as to minimize the sum of their magnetic and elastic energies. This deformation was studied in the smectic C phase of di-n-heptyloxyazoxybenzene using E.S.R. spectra of a spin probe dissolved in the mesogen. The samples consisted of slabs 20 µm to 200 µm thick, between glass surfaces, and their spectra were studied as function of the orientation and intensity of the magnetic field. Thin samples behaved as single crystals under rotation but the thicker samples exhibited elastic deformation. The results are quantitatively interpreted in term of a recent theory of the magnetic instabilities of smectic C [1], and the elastic constant for reorientation of the director is derived. The behaviour of multidomain samples of smectic C in magnetic fields is also discussed.