Self-bias ferromagnetic resonance and quasi magnetic isotropy of [FeCoB/MgO]6 multilayers prepared by composition gradient sputtering

Soft magnetic films (SMFs) are key materials for miniaturization and multifunctionality of radio frequency and microwave components and integrated circuits (ICs) due to the good high-frequency soft magnetic performances and the compatibility to IC processing technologies. Magnetic micro-inductors are one of widely used microwave IC components. The SMFs in magnetic micro-inductors should have a well-defined in-plane uniaxial magnetic anisotropy in order to reach a high ferromagnetic resonance frequency f_FMR. On the other hand, a high permeability is only available when excitation magnetic field being along the magnetic hard-axis (HA) direction, i.e. HA excitation. However, the typical planar micro-inductors are round or square, the magnetic anisotorpy characterisitics of the SMFs above indicates that the efficiency of SMFs can only reach 50% in inductors. Although many attempts have been made to enhance the efficiency of SMFs in inductors,¹ 100% HA excitation is still difficult to be reached.