Exchange coupling energy determined by ferromagnetic resonance in 80Ni-Fe/Cu multilayer films

Ferromagnetic resonance (FMR) experiments were carried out for [80Ni-Fe(60 Angstrom)/Cu(d(Cu) Angstrom)](N), (d(Cu) = 10-12, N = 2-5) multilayer films fabricated by a sputtering method. The main resonance peak had a broad shoulder located on the higher magnetic field side. Namely, the exchange energy between the magnetic layers was antiferromagnetic. In order to estimate the exchange energy, the FMR absorption spectrum was calculated using the Landau-Lifshitz equation of motion. The calculation model was improved so that we were able to analyze the spectrum for a multilayer with N magnetic layers. The exchange energy obtained from FMR analysis was compared with that estimated from the saturation magnetic field in the magnetoresistance (MR) curve. The positions and the intensity ratio of the resonance peaks were dependent on merely the exchange energy but not on the number of layers. The MR ratio was roughly proportional to the exchange energy.