Exchange Bias in NiCo/FeMn Bilayers with Stripe Domains

Exchange bias in NiCo/FeMn bilayers is established by alternating current (magnetic) field cooling, and stripe domains are induced as manifested by the ``double'' hysteresis loop. Only one resonance peak occurs at high magnetic fields in the in-plane ferromagnetic resonance spectra. The exchange field measured by both the magnetometry and ferromagnetic resonances is inversely proportional to the ferromagnetic layer thickness t_FM. More remarkably, the exchange field determined by the ferromagnetic resonance is smaller than that of the magnetometry measurements. It is suggested to arise from the misalignment of the unidirectional anisotropic directions in neighboring domains.