Magnetic (Fe1-xCox)(59)Pt-41 alloy thin films were deposited on Si substrate by sputtering. The surface morphology of (Fe1-xCox)(59)Pt-41 (x=0, 0.1, 0.2, 0.9) films changes with increasing Co content. The saturation magnetization was improved as the Co content increased, while the squareness and the coercivity decreased. The transformation temperature of a complete ordered fct phase rose as the Co content increased. By introducing a Cr underlayer, changes of the (Fe1-xCox)(59)Pt-41/Cr surface morphology are no longer observed as x increased. The perpendicular coercivity also increased from 6680 to 9220 Oe. (C) 2004 Elsevier B.V. All rights reserved.