Effect of ion-beam gas species on magnetic softness in Fe-Co thin-film etching

The effect of ion-beam (IB) gas species on magnetic softness in etching of Fe-Co thin films was evaluated by means of in situ magnetoresistance (MR) measurements. A 25-nm Fe₇₀Co₃₀ film was etched by Ar, Ne, or Kr IB, and successive MR measurements were performed in the same IB etching chamber. The IB etching and MR measurements were performed alternately in vacuum; therefore, it was possible to evaluate the etching gas effect on magnetic softness of the single sample in nanometer scale without the need to deposit a capping layer. Higher energy IB of 600 V showed larger gas species dependence of the deterioration than lower energy of 250 V. In the case of 600-V etching, Kr IB showed better softness compared with those of Ar and Ne IBs, whose etching surface was the smoothest among the etching conditions. Structural analysis revealed that surface roughness has an important role for magnetic softness and MR ratio in the thinner region of less than about 5 nm.