Stochastic inertial dynamics of the magnetization of nanoscale magnets subjected to a strong external magnetic field
Phys. Rev. B 111, 224425 – Published 23 June, 2025
DOI: https://doi.org/10.1103/1wrw-g3v9
Abstract
The inertial magnetization diffusion of magnetic nanoparticles in a strong external dc magnetic field in the presence of thermal noise is studied. A method of calculation of the transient response of a magnetization due to a sudden change in the external field is presented. The method is based on the simplification of the inertial Fokker-Planck equation by using the Fourier transformation with respect to the angular velocities, and then representing the resultant equation in operator form using angular momentum operators. The infinite hierarchy of differential-recurrence relations for the decay functions describing the relaxation of the system is derived. The solution of this hierarchy is obtained in terms of matrix continued fractions. The longitudinal dynamic magnetic susceptibility of the system is obtained as a particular case of the general method and analyzed for typical values of the model parameters. The high-frequency part of the longitudinal susceptibility spectrum in the region of nutation resonance can be approximated by a single Lorentzian. Comparison of the exact solution with the predictions of the analytical Lorentz formula demonstrates very good agreement. The effect of inertia on the magnetic properties of magnetic nanoparticles subjected to a strong external field in the presence of thermal noise is discussed.
