Magnetic anisotropy and resonance frequency of patterned soft magnetic strips

FeTaN thin films of 100nm with in-plane uniaxial anisotropy were fabricated by rf magnetron sputtering and patterned into strips with width varied from 30to500μm along both the easy and hard magnetization axes of the unpatterned films. The values of effective magnetic anisotropy of the patterned films increase as the strip widths decrease. The ferromagnetic resonance frequency showed a corresponding increment from 1.38to2.58GHz as the strip width varied. It indicates that this method is effective to tune the ferromagnetic resonance frequency of magnetic thin films. The resultant permeability spectra were understood according to the well-known Kittel formula where an averaged shape anisotropy arisen from the patterning was taken into account for the strips patterned along the easy axis. For the strips patterned along the hard axis, the increase in resonance frequency in narrower strips is attributed to the strengthened internal domain pinning effect predicted from the domain patterns numerically calculated.