Dynamics of the exchange field supplied by MnIr layers studied by network analyzer ferromagnetic resonance

We study the interlayer exchange phenomenon in MnIr/permalloy and MnIr/CoFeB thin films. Using network analyzer ferromagnetic resonance, we determine the interlayer exchange field acting on the ferromagnetic layer at each point of its hysteresis loop. These exchange fields indicate that the exchange bias value extracted from the back and forth coercivities does not describe correctly the magnitude and time evolution of the interlayer exchange field upon reversal of the ferromagnet magnetization. In particular for CoFeB layers, the interlayer exchange field can vary by 60% in a small applied field span at 300 K, which foreseen consequences for device reliability. (C) 2009 American Institute of Physics. [doi:10.1063/1.3225572]