Effect of a bias field on the longitudinal dynamic magnetic susceptibility of uniaxial antiferromagnetic nanoparticles

Abstract

This paper develops a kinetic theory of the low-frequency (far from the microwave range) longitudinal linear magnetic response of uniaxial antiferromagnetic nanoparticles. The proposed formalism is based on the Fokker-Planck-type equation for the distribution function of orientations of the antiferromagnetic vector. For this equation, a method of numerical solution is developed for the situation when a harmonic linearly polarized magnetic field and a constant bias field are co-aligned and applied along the anisotropy axis of the particle. Frequency dependencies of the real and imaginary parts of the longitudinal dynamic magnetic susceptibility of the particle are calculated for different values of the bias field magnitude. It is shown that in the presence of a constant field the magnetic response of the particle to a probing field decreases and the absorption maximum shifts to higher frequencies. Provided that the bias field is non-zero, the position of the specified maximum is not fixed but changes with the value of the uncompensated magnetization. It has been established that in the low frequency range, dispersion of the longitudinal dynamic magnetic susceptibility of the uniaxial antiferromagnetic nanoparticle is determined by a single Debye-type term.