Dynamic susceptibilities of an assembly of dipolar particles in an elasticenvironment - art. no. 031402

Theoretical model to describe magnetodynamics of a ferrogel, i.e., an assem bly of ferromagnetic nanoparticles embedded in a gel, is proposed. The reor ientations of the particles are determined by the influence of the elastic matrix and the rotational Brownian motion. Due to the interplay between the se two factors, the main parameter characterizing the static magnetic susce ptibility of the system is the ratio of the elastic modulus of the matrix t imes particle volume to the thermal energy. It is shown that the main compo nents of the dynamic magnetic-susceptibility tensor are determined by the c ombinations of the reference rates of several processes inherent to the sys tem, namely, the elastic restoration of the particle orientation, Brownian rotary diffusion, and viscous relaxation of the particle angular momentum. In the framework of the model, absorption of the energy of an alternating e xternal field by a ferrogel is studied. With allowance for the ever present interaction of elastic and Brownian forces, the effective relaxation times for the longitudinal and transverse components of the ferrogel magnetizati on are evaluated.