Influence of the Fe content on the Gd magnetic ordering temperature in Ni(sub1-x)Fe(subx)/Gd multilayers

We explore the influence of Fe content on the interfacial magnetic properties of Ni${}_{1\ensuremath{-}x}$Fe${}_{x}$(50 \AA{})/Fe ($t$ \AA{})/Gd(50 \AA{})/Fe ($t$ \AA{})/Ni${}_{1\ensuremath{-}x}$Fe${}_{x}$(50 \AA{}) ($x$ $=$ 0.2 and 0.6, and $t$ $=$ 0 and 10 \AA{}) multilayers by means of element-specific x-ray magnetic circular dichroism measurements at Gd M${}_{5}$ and (Ni, Fe) L${}_{2,3}$ absorption edges, superconducting quantum interference device magnetometry, and specular reflectivity measurements. Increasing Fe content in the Ni-Fe layer enhances the Gd ordering temperature in the interfacial regions. Addition of a 1-nm Fe spacer results in the largest enhancement in Gd ordering temperature in both interior and interfacial Gd regions, even for high Ni content in the Ni-Fe layer. This indicates that the Fe spacers act as effective barriers (albeit imperfect) in reducing Gd-Ni contact interactions responsible for limiting the interfacial Gd magnetic ordering temperature to values larger than bulk Gd, but significantly lower than observed at Fe/Gd interfaces.