<p>Interdiffusion studies and the formation of new phases in multilayer films have attracted interest both as a method for synthesizing new intermetallic compounds and in assessing the stability of layered structures used in microelectronics. The effect of low-temperature annealing on the state of Co/Pd multilayer film nanostructures with a cobalt layer thickness of 10 nm and palladium thicknesses of 0.5, 1, 2, 3 and 4 nm was studied using the ferromagnetic resonance method. The Co(Pd) solid solution phase formed as a result of annealing affects the ferromagnetic resonance field in a qualitatively different way, depending on the thickness of the initial Pd layer. In films with a Pd layer thickness greater than 2 nm, the resonance field increases, while at smaller thicknesses it decreases. An estimate of the activation energy of the process leading to the formation of a solid solution, 38 kJ mol⁻¹, indicates the diffusion character of the atomic transfer.</p>