Non-isochronicity of ferromagnetic nanoparticles of various shapes in a magnetic field

The possibility of controlling the non-isochronicity of ferromagnetic nanoparticles using an external magnetic field is investigated. Analytical expressions characterizing the nonlinear frequency shift of resonant magnetization oscillations for the diagonal tensor of demagnetizing factors are obtained by the method of Hamiltonian formalism. It is shown that when rotating and changing the magnitude of the vector of the external field of the bias magnetic field, it is possible to achieve a restructuring of the resonant oscillation frequency by changing the amplitude of the applied alternating magnetic field for both spherical and cylindrical the sample in the presence of uniaxial anisotropy. In the isotropic case, for a spherically symmetric sample, the non-isochronicity coefficient is zero due to the symmetry of the demagnetization tensor of the sphere, whereas for a cylindrical sample it is nonzero. The results obtained can be used to construct new types of essentially nonlinear microwave spintronics and magnonics devices.