The antiferromagnetic (AFM) interlayer coupling effective field in the ferromagnetic/non-magnetic/ferromagnetic (FM/NM/FM) sandwich structures, as a driving force, can dramatically enhance the ferromagnetic resonance (FMR) frequency. Changing the non-magnetic spacer thickness is an effective way to control the interlayer coupling type and intensity, as well as the FMR frequency. In the study, FeCoB/Ru/FeCoB sandwich trilayers with Ru thickness (t Ru ) from 1 to 16 Å were prepared by a compositional gradient sputtering (CGS) method. It was revealed that a stress induced anisotropy is present in FeCoB films due to the B composition gradient in the samples. A t Ru dependent oscillation of interlayer coupling from FM to AFM with two periods was observed. An AFM coupling occurs in the range of 2 Å ≤ t Ru ≤ 8 Å and over 16 Å, while a FM coupling is present in the range of t Ru < 2 Å and 9 Å ≤ t Ru ≤ 14.5 Å. It is interesting that an ultrahigh optical mode (OM) FMR frequency in excess of 20 GHz was obtained in the sample with t Ru = 2.5 Å under an AFM coupling. The dynamic coupling mechanism in trilayers was simulated, and the corresponding coupling type at different t Ru was verified by Layadi's rigid model. This study provides a controllable way to prepare and investigate the ultrahigh FMR films.
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).
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