Substantially enhancing ferromagnetic resonance frequency via superposition of composition gradient sputtering and magnetoelectric coupling in FeCoAlO/PZN–PT heterostructures

• A superposition method was proposed to improve the performance of magnetic films.
• The large anisotropy fields caused by the composition gradient and magnetoelectric coupling.
• A significant incensement of anisotropy and ferromagnetic resonance were achieved.
• The anisotropy field was up to 735 Oe and the ferromagnetic resonance frequency over 9.6 GHz.

Various methods were proposed to enhance the magnetic anisotropy field HK and ferromagnetic resonance frequency fFMR of soft magnetic films (SMFs), however, the values of HK and fFMR were still relatively low for the samples prepared by a single method alone. To further enhance the microwave ferromagnetic performances, in this paper, we proposed a superposition method in which the directions of uniaxial stresses induced by composition gradient and magnetoelectric coupling were designed to be parallel to each other, so that two individual HK added up. As a result, the HK was dramatically increased from 100 Oe to 735 Oe, and the fFMR from 3.4 GHz to 9.6 GHz in FeCoAlO/lead zinc niobate–lead titanate (PZN–PT with composition of 0.93Pb(Zn1/3Nb2/3)O3–0.07PbTiO3) multiferroic heterostructures. This superposition method showed big advantage over any of the single method, therefore was a promising method for preparing high-performance microwave SMFs with fFMR in excess of X-band.