Temperature-dependent spin-wave behavior in Co/CoO bilayers studied by Brillouin light scattering

We report Brillouin light scattering measurements of spin-wave frequencies in exchange coupled ferromagnet (FM)/antiferromagnet (AF) epitaxial Co/CoO bilayer structures. The ultrathin (7 Angstrom) CoO layer perturbs the Co la yer spin-wave frequencies and so permits a study of the influence of the AF CoO layer at the interface, when the unidirectional anisotropy is negligib le. A striking temperature dependence of the measured frequencies in the co balt layer in the range 77 to 300 K was observed which has been demonstrate d to be due to exchange coupling to the CoO layer as antiferromagnetic orde r develops. Furthermore, the existence of a uniaxial anisotropy field in th e range 100-300 Oe within the AF layer along the FM layer magnetization dir ection was demonstrated. The ratio of the interface to the bulk AF exchange coupling strengths was found to lie in the range 0.75 to 1.1. The observed temperature dependence of the spin-wave linewidths indicate that locally o rdered AF regions persist above the Neel temperature and play a central rol e in determining the magnetic behavior.