Effective anisotropy fields and ferromagnetic resonance behaviors of CoFe/PtMn/CoFe trilayers

Ferromagnetic (FM)/antiferromagnetic (AFM)/ferromagnetic trilayers of Ru seeded Co90Fe10/Pt50Mn50/Co90Fe10 and Co84Fe16/Pt50Mn50/Co84Fe16 were deposited, and their magnetic properties characterized at dc and at microwave frequencies. A ferromagnetic resonance (FMR) linewidth of 45 Oe at X-band (similar to 9.5 GHz) was achieved in the Co84Fe16/Pt50Mn50/Co84Fe16 trilayer. The minimum FMR linewidth occurs at an intermediate CoFe thickness, which is in contrast to the typical monotonic drop of FMR linewidth with the increment of FM layer thickness in the exchange-coupled FM/AFM bilayers. The CoFe/PtMn/CoFe trilayers show significantly enhanced anisotropy field up to 340 Oe at X band, which is more than double of that at dc frequency, indicating an obvious discrepancy between the anisotropy field at dc and at X band.