Dipole-exchange spin waves in magnetic thin films at zero and finite temperature: Theory and simulations

The excitation spectra in a stacked square lattice of dipole-exchange coupled classical spins is studied using both standard linearized spin-wave theory and the direct integration of the torque equation. A detailed comparison of the two methods is presented for the case of small-amplitude spin-wave modes. The spin-wave frequencies obtained from the time-dependent correlation functions calculated by integrating the equation of motion are shown to be in excellent agreement with the results obtained from linearized spin-wave theory for both single-layer and multilayer films. Applying the numerical integration method, the finite-temperature correlation function is calculated using Monte Carlo spin dynamics for the case of a single-layer, dipole-exchange coupled system. Values for the frequencies, amplitudes, and decay constant of the spin-wave modes at finite temperature are calculated from a spectral analysis of the finite-temperature correlation function. It is shown that thermal fluctuations give rise to a softening of the spin-wave frequencies and an intrinsic damping of the spin-wave oscillations.