  The in-plane dynamics of ferrimagnetic Co/Gd multilayers are investigated by
means of ferromagnetic resonance, magneto-optical Kerr effect and SQUID
magnetometry. The power absorbed from these multilayers is strongly temperature
dependent. For example, the resonant peak for a (Co 40 A /Gd 40 A)8 multilayer
vanishes approximately 50 K below room temperature. We have further
investigated Gd/Co/Gd and Tb/Co/Tb trilayers with different thicknesses of Gd
(5-7 A), Tb (1-7 A) and Co (30-40 A). At room temperature, these Co-based
trilayers show a shift of approximately 600 Oe at 24 GHz in the uniform
ferromagnetic resonance field, compared to pure Co film, indicating the
exchange coupling between the Co and Gd. The shift in the field for the
resonance increases as the temperature is decreased. Furthermore the resonance
linewidth increases as the temperature is decreased. The experimental results
are in good agreement with our theoretical calculations.
