Angular dependence of the exchange bias obtained from magnetization and ferromagnetic resonance measurements in exchange-coupled bilayers

Theoretical calculations of the angular dependence of the exchange bias field in ferromagnetic/antiferromagnetic bilayers were carried out in the framework of a model assuming the formation of a planar domain wall at the antiferromagnetic side of the interface with the reversal of the ferromagnetic orientation. The calculations were performed for various exchange interaction field strengths and for both cases of ferromagnetic and antiferromagnetic coupling. Analytical expression for the angular dependence of the ferromagnetic resonance field was obtained as well. It was shown that the exchange bias field variations derived from ferromagnetic resonance and hysteresis loop measurements become very close for strong interactions only. These field shifts, due to the different magnetization processes involved in the corresponding measurements, are different physical entities and, in general, must give different values.