Origin of coercivity in Co/Pt sputtered multilayers

Co/Pt multilayers have been prepared by rf magnetron sputtering onto glass substrates with negative bias voltage. For 0-V bias, the film consists of the columns grown perpendicular to the substrate and the convex interfaces between layers. The column boundaries and the convex interfaces act as the pinning center for the domain wall motion resulting in the high perpendicular coercivity, Hc(⊥ ). In the −30-V biased multilayers, the columns are fine and close packed, and thereby the layer interfaces are smooth and sharp. So that Hc(⊥ ) is very small in these multilayers. Higher bias voltage of −70 V causes the obscure interfaces and decreases the anisotropy energy. In the Co/Pt multilayer deposited on 0 V-Pt underlayer, the coercivity Hc(⊥ ) increases with thickness of 0 V-Pt underlayer and reaches 4 kOe at 1000 Å thickness. On the other hand, for −30 to −50-V Pt underlayer, the layer interfaces are smooth and sharp resulting in small Hc(⊥ ). Thus, Hc(⊥ ) is strongly affected by the film morphology such as the column boundaries or the layer interfaces.