High-frequency permeability of thin NiFe/IrMn layers

Thin permalloy films without and with an 8 nm IrMn exchange layer have been grown by sputter deposition. Permalloy thickness ranges from 15 nm to 50 nm. The microwave permeability of these layers has been investigated in the 50 MHz to 3 GHz range using a permeameter based on a microstrip cell. A satisfactory measurement precision is observed on permalloy films as thin as 15 nm. The gyromagnetic resonance frequency increases from 670 MHz for the unbiased sample, to 2.7 GHz for the thinner biased sample. This increase in frequency is slightly larger than expected from the exchange-bias field measured by Kerr effect using a simple model for the gyromagnetic behavior. The properties of a two-period superlattice are also reported.