Tuning microwave magnetic properties of composition gradient FeCoB/Ru/FeCoB trilayer films

FeCoB films were deposited by composition gradient sputtering, and an ultrathin Ru spacer was inserted in the middle of the 50 nm FeCoB films. The static and high frequency magnetic properties of the FeCoB/Ru/FeCoB trilayer films were systematically studied. The films show a good in-plane uniaxial anisotropy, and the anisotropy field increased greatly from 85 Oe to 417 Oe, while the corresponding resonance frequency was dramatically enhanced from 4.23 GHz to 8.36 GHz. Furthermore, the trilayer films also show a low damping of 0.012. This study provides a simple and effective technique to further increase the resonance frequency of soft magnetic films by inserting an ultrathin nonmagnetic spacer, which can be applied to high frequency microwave devices.