Nanocomposites and nanomaterials
Magneto-orientational effects in nematic liquid crystals 
doped with goethite nanoparticles
Burylov S.V.1, Lacková V.2, Tomašovičová N.2, Burylova N.V.1, 
Zakutanská K.2, Skosar V.Yu.1, Voroshilov O.C.1, Kopčanský P.2
1Institute of Transport Systems and Technologies of the NAS of Ukraine,
Pisargevskogo Str.,5,Dnipro -49005, Ukraine. E-mail: S.Burylov@nas.gov.ua
2Institute of Experimental Physics, Slovak Academy of Sciences, Watsonová 47, 04001 Košice, Slovakia
A review of our theoretical and experimental studies of orientation transitions arising under the influence of an external magnetic field in a nematic liquid crystal 6CHBT doped with magnetic lath-like goethite nanoparticles [1, 2] is presented. The magnetically induced behavior of this system strongly depends (i) on orientational coupling between nematic matrix and nanoparticles, (ii) on specific magnetic properties of goethite impurity, and (iii) on initial magnetic properties of the sample as a whole. It has been shown that the orientational coupling between nematic matrix and nanoparticles is determined by the anchoring forces between the nematic molecules and the magnetic nanoparticles, which are easily oriented by the external magnetic field. The direction of this orientation depends on the magnetic properties of goethite nanoparticles having two components of magnetic moments – the remanent magnetic moment along the main axes of the particles and the induced magnetic moment perpendicular to the main axes. Therefore, the nanoparticles tend to orient parallel and perpendicular to the external field in the low or high magnetic field region, respectively. The magnetic orientation effects are further influenced by the initial magnetic properties of the samples. Two types of samples with different magnetic properties were prepared. A zero initial magnetization sample was obtained after cooling the system from isotropic to nematic phase in the absence of a magnetic field. The magnetized sample was prepared during magnetic field application. These samples showed various magneto-orientational effects that were successfully described theoretically using the proposed continual approaches.
 
1.	Kopčanský P., Gdovinová  V., Burylov S., Burylova N., Voroshilov  A., Majorošová J., Agresti F., Zin V., Barison S., Jadżyn J., Tomašovičová  N. The influence of goethite nanorods on structural transitions in liquid crystal 6CHBT // J. Magn. and Magn. Mater.– 2018. – 459, P 26-32.
2.	Burylov S., Petrov D., Lacková V., Zakutanská K., Burylova N., Voroshilov A., Skosar V., Agresti F., Kopčanský P., Tomašovičová N. Ferromagnetic and antiferromagnetic liquid crystal suspensions: Experiment and theory// J. Mol. Liq.–2021.–321, 114467.