Dynamic response of interacting superparamagnetic particles with aligned easy magnetization axes

Abstract A theory of the dynamic magnetic response of an ensemble of immobilized ferroparticles on a weak, linearly polarized ac magnetic field is developed. All particles have uniaxial magnetic anisotropy and the particle easy magnetization axes are aligned in one direction. External ac field is oriented with some given angle to the easy axes. The interparticle dipole-dipole interaction is taken into account basing on the first order modified mean-field model, in the framework of which the orientation of the magnetic moment of a randomly chosen particle is influenced by an external magnetic field and by a total dipolar field produced by all other magnetic moments. The dynamic magnetic susceptibility and magnetization are calculated as a function of the frequency and direction of the field, as well as height of the magnetic crystallographic anisotropy energy barrier for internal superparamagnetic rotation of magnetic moments inside the particles.