Cumulative interface roughness and magnetization in antiferromagnetically coupled NiCo/Cu multilayers

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Abstract
Cumulative interface roughness and its influence on the magnetization process in antiferromagnetically coupled (Ni80Co20/Cu)×N multilayers is studied. In these multilayers, Cu and Ni80Co20 thicknesses are fixed at 20 and 15 Å, respectively, in order to obtain the antiferromagnetic coupling at the second oscillation peak of giant magnetoresistance (GMR) versus Cu thickness. Low‐angle x‐ray reflectivity measurements show that cumulative interface roughness increases with increasing bilayer number N. In‐plane magnetization hysteresis measured with both SQUID and surface magneto‐optic Kerr effect (SMOKE) magnetometers are compared. When the cumulative interface roughness is significant, SMOKE hysteresis loops, which are sensitive to the top 5 or 6 magnetic layers, display a nonlinear plateau region at small fields. Comparison of low‐angle x‐ray, and SMOKE results show that interfaces of relatively high quality in top layers only exist for sputtered multilayer with N<10.