Magnetic recording performance of cobalt-alloy perpendicular media depends upon microstructural features including preferred c-axis out-of-plane orientation, grain size and grain separation. These depend on the titanium-alloy underlayer surface structure, which in turn depends on film nucleation and growth. The Ti-alloy nucleation and growth stages are independently controlled by changing argon pressure during sputter deposition. Ti and Ti90Cr10 underlayers have qualitatively different microstructures, but in each case a two-step deposition process produces a better combination of separated magnetic layer grains and strong preferred orientation than constant argon pressure underlayer media. Correspondingly, media magnetic performance is improved over single pressure depositions. Observed microstructure and magnetic properties are consistent with simple growth models.