Kinetics of Domain Structure in Co/Pt/Co Ultrathin Films with Ferromagnetic Interlayer Exchange Interaction: Dependence on Interlayer Thickness

Abstract

We studied the in-field evolution of the domain structure in ultrathin Co(0.6 nm)/Pt(t)/Co(0.6) nm trilayers with perpendicular magnetic anisotropy for 5 nm < t < 6 nm using polar Kerr microscopy. The critical interlayer thickness tcr = 5.3 nm was found to separate two principal patterns of domain behavior including interlayer correlations and motility of the domain walls. It is shown that magnetization in both Co layers is coupled with strong ferromagnetic interaction for small Pt thickness (t < tcr), while this coupling is weak for thicker (t > tcr) Pt layers. Nonlinear dependence of the wall displacement on the field value is observed. The established final position of domain walls after relaxation depends on the Pt layer thickness. It is determined by balance of the interlayer exchange and energy gain due to the field. The mechanism of wall stabilization is considered in the case of independent wall motion. In the region with weak coupling, dependence of the interlayer interaction energy on Pt thickness was measured.