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RF/microwave soft magnetic films (SMFs) are key materials for miniaturization and multifunctionalization of monolithic microwave integrated circuits (MMICs) and their components, which demand that the SMFs should have higher self-bias ferromagnetic resonance frequency fFMR, and can be fabricated in an IC compatible process. However, self-biased metallic SMFs working at X-band or higher frequency were rarely reported, even though there are urgent demands. In this paper, we report an IC compatible process with two-step superposition to prepare SMFs, where the FeCoB SMFs were deposited on (011) lead zinc niobate–lead titanate substrates using a composition gradient sputtering method. As a result, a giant magnetic anisotropy field of 1498 Oe, 1–2 orders of magnitude larger than that by conventional magnetic annealing method, and an ultrahigh fFMR of up to 12.96 GHz reaching Ku-band, were obtained at zero magnetic bias field in the as-deposited films. These ultrahigh microwave performances can be attributed to the superposition of two effects: uniaxial stress induced by composition gradient and magnetoelectric coupling. This two-step superposition method paves a way for SMFs to surpass X-band by two-step or multi-step, where a variety of magnetic anisotropy field enhancing methods can be cumulated together to get higher ferromagnetic resonance frequency.

Ferromagnetic resonance (FMR) in soft magnetic films (SMFs) to a large extent determines the maximum working frequency of magnetic devices. The FMR frequency (fr) in an optical mode is usually much higher than that in the corresponding acoustic mode for exchange coupled ferromagnet/nonmagnet/ferromagnet (FM/NM/FM) trilayers. In this study, we prepared a 50 nm FeCoB film with uniaxial magnetic anisotropy (UMA), showing a high acoustic mode fr of 4.17 GHz. When an ultrathin Ru spacer was inserted in the very middle of the UMA-FeCoB film, the zero-field FMR was abruptly switched from an acoustic mode to an optical one with fr dramatically enhanced from 4.17 GHz to 11.32 GHz. Furthermore, the FMR mode can be readily tuned to optical mode only, acoustic mode only, or double mode by simply varying the applied filed, which provides a flexible way to design multi-band microwave devices.

Strong converse magnetoelectric coupling was observed in a multiferroic heterostructure of Fe59.3Co28.0Hf12.7 film on (011) cut lead zinc niobate-lead titanate (PZN-PT) slab, which exhibited a large electric field (E-field) tunability of microwave magnetic properties. With the increase of E-field from 0 to 6 kV/cm on PZN-PT, the ferromagnetic resonance (FMR) field Hr shifts downwards by 430.7 Oe along [011¯] direction and upwards by 492.9 Oe along [100] direction of the PZN-PT. Accordingly, the strong magnetoelectric coupling led to a significantly enhanced self-biased FMR frequency from 4.2 to 7.9 GHz under zero bias magnetic field, and the magnetic damping constant α was decreased from 0.0260 to 0.0185 at the same time. These features demonstrate that this multiferroic laminate is promising in fabrication of E-field tunable microwave components.

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A vortex magnetic anisotropy (VMA) was formed via the competition of residual stresses between radial and tangential directions in the FeCoAlO soft magnetic films (SMFs), prepared by a composition gradient sputtering (CGS) method. The VMA of the magnetic films gives rise to a rotating excitation direction of the ferromagnetic resonance. As a results, the as-deposited FeCoAlO films exhibit good high-frequency ferromagnetic properties with high permeability about 100, cut-off frequency over 2 GHz, and Qm factor over 50 along its individual excitation direction. These SMFs with the VMA are promising in the integration with the circular spiral inductors due to the geometrical match between the excitation direction of the SMFs and the circular inductor lines.