Magnetization reversal in [Ni/Pt]6/Pt(x)/[Co/Pt]6 multilayers

The magnetization reversal is studied in magnetron sputtered artificial superstructures of the form [Ni/Pt]6/Pt(x)/[Co/Pt]6 with perpendicular anisotropy, in which the [Co/Pt]6 stacks have higher coercivity than the [Ni/Pt]6. For x≥2 nm the two stacks reverse separately and exhibit characteristic stepped loops with a “plateau” in the region between the two switching fields. First-Order Reversal Curves (FORCs) reveal that the maximum coupling is obtained for x=1.5 nm. While each of the Ni/Pt and Co/Pt stacks by itself is thin enough to reverse in large domains when they are coupled, formation of maze like domains is observed. In this case some reversibility of the demagnetization curves associated with interfacial domain wall pinning appears while in the rest of the cases the reversal mechanism is based on lateral domain wall pinning with low reversibility. In the loops monitored by Extraordinary Hall Effect (EHE) measurements this “plateau” appears as a hump due to the different sign of the EHE coefficient between the [Ni/Pt]6 and [Co/Pt]6.

Research highlights► Magnetization reversal in perpendicular anisotropy superstructures [Ni/Pt]6/Pt(x)/[Co/Pt]6. ► Coupling between the (harder) [Co/Pt]6 and (softer) [Ni/Pt]6 stacks, adjusted by the thickness x of a Pt interlayer. ► Each of the Ni/Pt and Co/Pt stacks by itself is thin enough to reverse in large domains with low reversibility. ► When coupled, formation of maze like domains is observed and reversibility of the demagnetization curves associated with interfacial domain wall pinning appears. ► For x≥2 nm the two stacks reverse separately and exhibit characteristic stepped loops with a “plateau” that appears as a hump in EHE loops due to the different sign of the EHE coefficient of the two stacks.