Anisotropy patterning of amorphous CoFeSiB films by He -ion radiation

The alteration of magnetic properties in magnetic thin films by ion radiation has gained increasing attention in recent years. Most of the experiments focus on magnetic multilayers, e.g. Pt/Co [1] or exchange bias [2] systems. Only a few results are obtained from soft magnetic polycrystalline single-layer films [3] using Ga - ions. Here, we present data on the local alteration of the magnetic anisotropy axis in amorphous soft magnetic (Fe9090Fe10)78B10Si12 films by He -ion radiation in an applied magnetic in-plane field. Sputtered CoFeSiB (thickness 30 nm) were irradiated with 5 keV He -ions with a fluence ranging from 5 10^14 ions/cm2 to 5 10^16 ions/cm2. A magnetic field of 600 Oe was applied during irradiation aligned under an angle to the initial easy axis of anisotropy. Above a fluence of 1016 ions/cm2 a rotation of uniaxial anisotropy in the applied field direction in the irradiated areas is observed by MOKE magnetometry and complementary domain observation by Kerr microscopy in the longitudinal mode. No degradation in magnetic properties relative to the as-deposited state is found from the magnetization loops on non-patterned samples. The easy axis coercivity is typically around Hc,ea = 2 Oe and the anisotropy field around Hk = 18 Oe. Using irradiation together with photolithography the films were irradiated locally, thus resulting in "anisotropypatterned" structures. Domain patterns in differently anisotropy-patterned elements with varying angles of anisotropy and edge orientation, separating regions of different anisotropy alignment, are shown. The influence of the patterning on the (still) full film reversal and the resulting border domain structures are discussed in detail.
References:
[1] C. Chappert et al., Science 280, 1919 (1998)
[2] A. Mougin et al., Phys. Rev. B 63, 060409 (2001)
[3] Woods et al., Appl. Phys. Lett. 81(7), 1267-1269 (2002)