Magnetic easy-axis switching in Co/Pt and Co/Au superlattices induced by nitrogen ion beam irradiation

In this paper, the sputtering-grown [Au 6 nm/Co 0.5 nm] × 10 and [Pt 6 nm/Co 0.5 nm] × 15 superlattices are irradiated using N+ 150 keV ions with fluences ranging from 1012 up to 3 × 1016 N+/cm2. The effect of this ion irradiation experiment on perpendicularly magnetized Co/Au and Co/Pt superlattices is presented. Combining structural and magneto-optical measurements, we reveal the differences in the ion induced mixing between miscible Co–Pt and immiscible Co–Au layered systems. For Co/Pt ones, the progressive ballistic intermixing between Co and Pt leads to a decrease of perpendicular anisotropy and to an in-plane reorientation of the easy axis of magnetization. Although, for Co/Au superlattices the mixing occurs but a thermodynamic phase separation is observed. The structural investigations show that for high fluences the Co layers are disrupted in islands with few nanometer size embedded in Au layers. The perpendicular magnetic anisotropy decreases with fluence but no anisotropy reorientation appears.