Self-biased optical mode ferromagnetic resonance beyond 22 GHz in artificial exchange coupled trilayers

•FeCoB/Ru/FeCoB trilayers prepared by a CGS show strong AFM coupling.•A very strong exchange coupling field as high as 2235 Oe was obtained.•A record optical mode resonance frequency up to 22.68 GHz was achieved.•Resonance mode changing at a low field results in a large fr jump over 16 GHz. The ferromagnetic resonance frequency (fr) determines the maximum operating frequency of magnetic devices, nevertheless, it is very difficult to increase the fr(H=0) above 10 GHz by simply increasing the magnetic anisotropy field HK. In this study, a series of FeCoB/Ru/FeCoB sandwich trilayers with strong antiferromagnetic coupling were prepared by a compositional gradient sputtering method. As a result, the fr(0) increases from 13.69 to 22.68 GHz with the increase of B content, which can be attributed to the strong interlayer exchange coupling. In addition, a dramatic frequency shift over 16 GHz along easy-axis direction can be achieved simply via transition of magnetic configuration using a small magnetic field of the order of 100 Oe. This study provides an effective fabrication method to prepare self-biased soft magnetic films with ultrahigh resonance frequency for today’s microwave integrated circuits.