The magnetization and coercivity of Co films in the thickness range of 10-200 nm deposited onto GaAs (1 0 0) substrate are studied. The in-plane coercivity of the Co films is enhanced anomalously and is observed to have strong thickness dependency. The coercivity of the Co/GaAs having Co thicknesses larger than a threshold value (50 nm) is enhanced at 4.2 K. The Co film having thickness 50 nm exhibits a coercive field of 10 Oe, but the same for thickness 125 nm increases to 120 Oe. The squareness of the hysteresis loop becomes as high as 94%. The atomic magnetic moment of the Co film is found to be 1.5 μB. The AFM images show that surface roughness increases with the increases of film thickness. The enhancement of coercivity is due to the surface roughness of the Co film. © 2006 Elsevier B.V. All rights reserved.
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