A set of seed and underlayers for thin film perpendicular recording media has been optimized using a technique involving simultaneous thickness and composition gradients on a single test wafer. Magnetron sputtering under ultrahigh vacuum conditions in Ar gas was used for the deposition of the layers. The structure being optimized consisted of a Ta seed layer, RuxCo1-x, Co63Cr37 underlayers, and a Co68Cr18Pt8B6 hard magnetic layer. One of the layers in the stack on a wafer has been deposited so that both a thickness variation and composition variation occurred. The method allows cross terms between thickness and the individual compositional terms to be investigated. Coercivity and squareness of the samples was measured by magneto-optical Kerr rotation. The results showed that for the range of thickness under investigation, the highest coercivity and squareness does not occur for the same set of conditions. Maximum squareness is reached without a radio frequency (rf) bias, while the coercivity increases further with the application of a -25 V rf bias. © 2002 American Vacuum Society.