Spin wave frequency shifts in exchange coupled ferromagnet/antiferromagnet structures: Application to Co/CoO

Abstract

Co/CoO structures have been studied almost exclusively through measurements of hysteresis, and display an enhanced and strongly temperature dependent effective in-plane anisotropy. A recent experimental study demonstrated an alternate way of investigating effects related to the coupling across the interface by measuring frequencies of long wavelength spin waves associated with the Co film. A large increase in frequency of the low frequency spin wave in the Co was observed as the temperature was lowered through the Neél temperature of CoO. We show how these frequency shifts can be understood as an effective interface anisotropy introduced by strong exchange coupling across the Co/CoO interface. This means that spin waves in the Co also include energy contributions from the larger anisotropies experienced by spins in the CoO. The theory is presented and discussed for the Co/CoO interface and other structures.