Local coercivity at X-ray nanobeam irradiated regions in amorphous Fe80B20 stripes

We report on the effect, on the local magnetization reversal taking place in amorphous Fe80B20 stripes, of the irradiation with nanobeam synchrotron X-ray. That irradiation preserves the amorphous structure and results on the increase of the local coercivity with respect to that measured in a non-irradiated sample, in which the coercivity is mediated by the nucleation-propagation of a single wall. The local coercivity increases in a non-linear way with the width of the irradiated regions when that width is smaller than that of the wall mediating the magnetization switching in the non-irradiated stripe and gets saturated when the irradiated regions dimension is larger than the propagating wall width. We correlate this behavior with the induction at the irradiated regions of a reduction of the local effective anisotropy with respect to the stripe as-lithographed value. From the relationship between the coercivity and the width of the irradiated regions we estimate the local anisotropy reduction in a 25% of that measured in the non-irradiated stripe.