The description of the collective magnetorheological effect induced by
magnetic field in magnetoactive elastomers is proposed. The condition of
consistency is used between magnetic and mechanic momenta of forces exerted on
magnetically uniaxial ferromagnetic particles in elastomer at their
magnetization. The study shows that even in the case of small concentration of
particles, the value of magnetically-induced shear can be anomalously large,
reaching up to tens of percent. The deformation of magnetoactive elastomer can
evolve critically, as a second-order phase transition, if magnetic field is
aligned along the easy axis of particles.Comment: 9 pages, 3 figure