Dynamic interlayer exchange coupling in magnetic anisotropic FeCoB/Ru/FeCoB sandwich trilayers

Abstract Transverse and longitudinal vector network analyzer ferromagnetic resonance (VNA-FMR) spectroscopy, which can easily distinguish the optical and acoustic modes of FMR, is used to study the dynamic interlayer exchange coupling (IEC) in the oblique sputtered Fe56Co24B20(26.5 nm)/Ru( t Ru )/Fe56Co24B20(26.5 nm) trilayers with various Ru thicknesses t Ru . Comparing with the static IEC research method, the dynamic method not only analyzes the frequency response characteristics caused by IEC, but also identifies the nature of IEC. In the studied system, an oscillatory interlayer coupling shows up in the VNA-FMR dynamic measurement. An antiferromagnetic (AFM) coupling appears at 0.35 nm t Ru ≤ 0.9 nm, while a strong ferromagnetic coupling dominates at t Ru ≤ 0.3 nm and a weak ferromagnetic coupling dominates at t Ru ≥ 1 nm. The strongest AFM coupling with coupling coefficient J1 of -0.87 erg/cm2 occurs at the intermediate thickness of t Ru ∼0.5 nm, while a strong FM coupling with J1 as large as 1.1 erg/cm2 dominates in the relatively thin 0.23 nm Ru spacers. The coupling mechanism is simulated with Layadi’s rigid model and the oscillatory behavior of the bilinear IEC coefficient J1 versus t Ru is obtained.