In situ magnetoresistance measurements of ion-beam-etched Fe-Co thin films

The effect of ion-beam (IB) irradiation on magnetic softness in Fe-Co thin films was evaluated by means of in situ magnetoresistance (MR) measurements. A 25 nm Fe70Co30 film was etched by Ar IB, and successive MR measurements were performed in the same IB etching chamber. Since the IB etching and MR measurements were performed alternately in vacuum, it was possible to evaluate the etching effect on magnetic softness of the single sample without any capping layer interaction. We name the thickness below which the magnetic softness of the etched film starts to decrease as the critical thickness (Tcr). The Tcr was found to be affected by IB energy: 150 and 250 V IB, respectively, showed 7.5 and 10 nm smaller Tcr than that of 600 V IB. Structural analysis revealed the 600 V IB introduced a larger deterioration in the film crystallinity than with the 250 V IB.