FMR Damping in Thin Films with Exchange Bias

Abstract

Ferromagnetic resonance (FMR) linewidth (LW) is a tool for studying the high frequency properties of magnetic materials for their application in high-speed devices. Here, we investigate different mechanisms which determine FMR damping in bilayer ferromagnetic/antiferromagnetic (F/AF and AF/F) exchange bias systems. Variations of FMR LW with the thickness and deposition order of the F and AF layers were studied, as well as their correlation with the exchange bias field and roughness of the sample surface. We observed much larger LW in AF/F structures compared with F/AF samples. It was found that neither the exchange bias nor surface/interface roughness in the samples could explain the difference in LW for F/AF and AF/F samples. Instead, the different underlayer microstructure influenced the grainsize, leading to different angular dispersion of magnetization and different internal stray field in F-layers, promoting a different intensity of magnon scattering and FMR damping in F/AF and AF/F samples.

Temperature Dependence of Magnetization Dynamics in Co/IrMn and Co/FeMn Exchange Biased Structures

“…where the surface anisotropy Hn pushes magnetization vector M out of the film's plane as suggested in [19,45]. An alternative explanation of lowering the effective magnetization is an angular spread of magnetic moment due to an angular spread of uniaxial anisotropy in nanocrystalline microstructure of Fe-layers [46]. A non-complete averaging of magnetocrystalline anisotropy during the F-layer deposition causes residual spread of uniaxial anisotropy around the EA, leading to a stray field and local oscillation of magnetization [47,48], which is observed as a ripple structure in a defocused film image in the Lorentz transmission electron microscopy (LTEM) in the Fresnel mode [49][50][51].…”