Dry-etching damage to magnetic anisotropy of Co-Pt dot arrays characterized using anomalous Hall effect

Using high-resolution e-beam lithography and ion beam etching, dot arrays were formed from Co–Pt alloy films with perpendicular magnetization. Dry-etching damage to uniaxial magnetic anisotropy Ku of the fabricated dot arrays was examined. Hcp–Co75Pt25 films and L11-type Co50Pt50-ordered alloy films with film thickness δ of 3, 5, and 10 nm were used for this study. Dot diameter D was varied from 10 nm to 400 nm. The effective magnetic anisotropy of the dots, Kueff, was measured using the generalized Sucksmith–Thompson method with anomalous Hall effect (AHE) and an averaged AHE signal over 100–71,000 dots. By compensating the dot shape anisotropy, Ku was calculated from Kueff. The Ku for a dot array of D = 400 nm was almost equal to that for an original continuous film, but Ku decreased gradually for D < 30 nm. The circumferential area (periphery) of dots with width WD was assumed to be damaged by etching. The damaged area was inferred as Ku = 0 with original saturation magnetization Ms. The WD values, as estimated using experimental data, were 1.6–1.8 nm for hcp–Co75Pt25 dot arrays independent of δ (δ = 3–10 nm) and 1.8–1.9 nm for L11–Co50Pt50 dot arrays (δ = 3–5 nm). For all dot arrays, Ku at D = 10 nm were nearly half those for the original continuous films, suggesting that films having Ku of twice that for original films were necessary to overcome Ku reduction by etching damage.