Susceptibility of the disordered system of fine magnetic particles: a Langevin-dynamics study

Using the Langevin dynamics, we have calculated numerically the temperature and concentration dependence of the complex alternating-current susceptibility χ(ω, T ) for disordered systems of fine magnetic particles taking into account the dipolar interparticle interaction. We demonstrate that the behaviour of the χ(ω, T ) dependencies with increasing particle concentration (which means increasing interaction strength) and with increasing frequency depends qualitatively on the single-particle anisotropy and on the damping parameter used in the corresponding Langevin equation.