Enhancement of high-frequency performances by Al2O3 interlayer in FeCoHf/Al2O3/FeCoHf trilayers

In this study, Hf-doped FeCo alloy films with a high ferromagnetic resonance (FMR) frequency at zero external fields were prepared by a composition gradient sputtering method. In order to further enhance the high-frequency performances, Al2O3 spacers of various thicknesses were inserted in the middle of the FeCoHf film. It is revealed that the Al2O3 interlayer improves the magnetic anisotropy of trilayers, enhances the resistivity, and refines the grain size. As a result, the FMR frequency of the trilayer was enhanced to over 3 GHz, and the permeability was also evidently improved from 41 (single layer) to 86 (trilayer with Al2O3 thickness of 40 Å).