Orientation control of optical mode ferromagnetic resonance: From uniaxial to omni-directional

Both high ferromagnetic resonance frequency ( f r) and homogeneous angular performance are important for soft magnetic films to be used in high-frequency integrated circuit devices. However, high f r are obtainable only along the easy axis direction of the magnetic anisotropic materials. In uniaxially anisotropic FeCoB/Ru/FeCoB films, we could obtain an ultrahigh optical mode ferromagnetic resonance frequency ( f r O) up to 19.16 GHz along the easy axis under a self-bias field due to the enhancement from strong interlayer exchange coupling. However, the uniaxial intensity distribution of optical mode resonance seriously hinders the practical application in microwave components. In order to obtain the desired homogeneous angular performance, soft magnetic films with widely distributed magnetic anisotropy directions in the films were prepared and a nearly omni-directional f r O with uniform values around 13.5 GHz was achieved. This study demonstrates that controlling the magnetic anisotropy's angular distribution is an effective way to obtain isotropic, self-bias magnetic films with ultrahigh f r.