Brillouin light scattering spin wave studies show that the frequency and linewidth of ultrathin Co/CoO films are strongly dependent on the temperature, so that when the temperature increases, both the frequency and linewidth decrease. In this paper, the frequency and linewidth in Co/CoO films are considered theoretically. We consider the case of coupled ferromagnetic and anti-ferromagnetic films with the exchange coupling at the interface weak compared to the intra-film exchange. The frequency is calculated as two coupled spins with weak exchange coupling. The magnetic fields applied on each spin are the effective magnetic fields on Co in metallic Co and in CoO. Fluctuations in the interface give rise to a random field that causes the additional linewidth. Within this model we can explain the observed increase of the frequency and linewidth with decreasing temperature.

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