Magnetic relaxation in exchange-coupled Co/CoO bilayers measured with ac-anisotropic magnetoresistance

The perturbation of magnetization with a small ac field was used to measure the complex ac-susceptibility of field-cooled Co/CoO bilayers. Samples of Ta(3 nm)/Co(8 nm)/CoO(3 or 10 nm)/Cu(3nm) grown by sputter deposition on an amorphous silicon nitride substrate was also studied using a frequency of 100 Hz. The real and imaginary response showed prominent thickness-dependent peaks at the blocking temperature.