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 chi (omega, T) for disordered systems of fine magnetic particles taking into account the dipolar interparticle interaction. We demonstrate that the behaviour of the chi (omega, 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.