Effect of Seed Layer Annealing on Perpendicular Magnetic Anisotropy in Pt/Co/Pt Trilayers Deposited on Si Substrates With Cu Seed Layers

Pt/Co/Pt trilayers with perpendicular magnetic anisotropy (PMA) were deposited onto Si substrates with Cu seed layers, which were thermally annealed at various temperatures to alter their surface roughness. Annealing at temperatures up to $475~^{\circ }$ C induced significant grain growth in the 5 nm thick Cu seed layer, substantially increasing its surface roughness. At $500~^{\circ }$ C, the root-mean-square (rms) roughness of the Cu seed layer surpassed the 0.8 nm thickness of the Co layer, potentially disrupting its continuity. This increased surface roughness created pinning sites that significantly enhanced coercivity—up to approximately 430% compared to the as-deposited trilayer—by impeding domain wall motion. However, the excessive roughness at $500~^{\circ }$ C weakened ferromagnetic exchange interactions between Co spins, diminishing PMA and coercivity. Magnetic domain images revealed that the increasing Cu layer roughness promoted the formation of new domain nucleation sites while reducing domain wall velocity. These findings demonstrate that the perpendicular magnetic properties of the Pt/Co/Pt layer can be controlled by the microstructural characteristics of the underlying seed layer.