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 K-u of the fabricated dot arrays was examined. Hcp-Co75Pt25 films and L1(1)-type Co50Pt50-ordered alloy films with film thickness delta 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, K-u(eff), 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, K-u was calculated from K-u(eff). The K-u 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 W-D was assumed to be damaged by etching. The damaged area was inferred as K-u = 0 with original saturation magnetization M-s. The W-D values, as estimated using experimental data, were 1.6-1.8 nm for hcp-Co75Pt25 dot arrays independent of delta (delta = 3-10 nm) and 1.8-1.9 nm for L1(1)-Co50Pt50 dot arrays (delta = 3-5 nm). For all dot arrays, K-u at D = 10 nm were nearly half those for the original continuous films, suggesting that films having K-u of twice that for original films were necessary to overcome K-u reduction by etching damage. (C) 2012 American Institute of Physics. [doi:10.1063/1.3676061]