Ferromagnetic coupling between Co layers in Co/Pt multilayer with perpendicular anisotropy

A series of glass/NiO(lnm)/[Co(0.4nm)/Pt(0.5nm)]₃/Pt(xnm)/[Co(0.4nm)/Pt(0.5 nm)]₃ samples with different Pt interlayer thicknesses were prepared by magnetron sputtering to determine the ferromagnetic coupling between Co layers across the Pt layer. The measured results of major and minor hysteresis loops show that the ferromagnetic coupling between the top and bottom Co/Pt multilayer decreases monotonously with the increase of Pt layer thickness and disappears as the Pt layer thickness over 4 nm. In addition to the ferromagnetic coupling, there exists a weak biquadratic coupling, which induces the broad transition of the bottom Co/Pt multilayer.