Frederiks transition in magnetic suspensions

The Frederiks effect was studied in the suspension of nematically ordered n eedlelike ferromagnetic particles with account for their steric and magneti c interactions. It was revealed that the critical field increases with part icle concentration and the degree of particle extension, whereas the amplit ude of nematic structure deformation decreases. The enhancement of magnetic interparticle interaction results in a decrease of the critical field and in an increase in deformation amplitude. The Frederiks effect was accompani ed by particle segregation in the slit center, which was larger the stronge r the particle magnetic interaction was. Calculations showed that under def inite conditions, the Frederiks effect in the suspensions of hard polar par ticles may be implemented as a first-order rather than a second-order trans ition. The initial transition stage was studied. It was demonstrated that i f the magnetic field exceeded a certain critical value (larger than the cri tical field of equilibrium transition), the Frederiks effect was accompanie d by the appearance of noneqiulibrium periodic structures with different or ientations of the nematic director. A similar effect was observed when the permanent magnetic field was reversed.