Design of Nuclear and Magnetic Scattering Length Density Profiles

The scattering length density (SLD) profile of a sample can be deliberately designed to enhance the information of interest obtained from neutron reflectometry. Here, we demonstrate this approach using amorphous ${\mathrm{F}\mathrm{e}}_x{\mathrm{C}\mathrm{o}}_y{\mathrm{A}\mathrm{l}}_8{\mathrm{Z}\mathrm{r}}_2$ thin films. Four samples, each comprising ten repetitions of an AlZr spacer layer and a magnetic layer, were prepared with magnetic-layer compositions of ${\mathrm{F}\mathrm{e}}_{80}{\mathrm{C}\mathrm{o}}_{10}{\mathrm{A}\mathrm{l}}_8{\mathrm{Z}\mathrm{r}}_2$, ${\mathrm{F}\mathrm{e}}_{70}{\mathrm{C}\mathrm{o}}_{20}{\mathrm{A}\mathrm{l}}_8{\mathrm{Z}\mathrm{r}}_2$, ${\mathrm{F}\mathrm{e}}_{60}{\mathrm{C}\mathrm{o}}_{30}{\mathrm{A}\mathrm{l}}_8{\mathrm{Z}\mathrm{r}}_2$, and ${\mathrm{F}\mathrm{e}}_{45}{\mathrm{C}\mathrm{o}}_{45}{\mathrm{A}\mathrm{l}}_8{\mathrm{Z}\mathrm{r}}_2$, and characterised using X-ray and polarised neutron reflectometry. Across the series, the nuclear SLD of the FeCoAlZr alloy decreases approximately linearly from $7.14\times {10}^{-6}$ to $4.63\times {10}^{-6}$ ${\mathring{\mathrm{A}}}^{-2}$ with increasing Co content, while the magnetic SLD is approximately $4.3$-$4.5\times {10}^{-6}$ ${\mathring{\mathrm{A}}}^{-2}$. These results demonstrate that the nuclear and magnetic contributions can be controlled largely independently, with composition primarily tuning the nuclear SLD and the applied magnetic field offering, in principle, additional control of the magnetic contribution.