Microwave and DC anisotropy fields of exchange-coupled CoFe/PtMn/CoFe trilayers

摘要

Exchange-coupled antiferrromagnetic(AFM)/ferromagnetic(FM) bilayers and FM/AFM/FM trilayers show enhanced anisotropy fields due to the exchange coupling[1-4], and are excellent candidates for RF and microwave applications[5,6]. However, strong exchange coupling typically leads to enhanced ferromagnetic resonance (FMR) linewidth[1-4], which is undesired for many microwave applications. It was recently found that FM/AFM/FM tri-layer CoFe/PtMn/CoFe sandwich films showed a minimum FMR linewidth of 45Oe at an intermediate magnetic layer thickness (tF)[7], which was unexpected according to our knowledge on exchange coupled FM/AFM bilayers. In this paper, we examined the FMR characteristics of CoFe/PtMn/CoFe trilayer thin films to determine mechanisms behind the intermediate drop in linewidth observed, and investigate the exchange bias fields (Hex) at DC versus at X-band (9.5GHz).