Modification of thickness dependent magnetic properties of perpendicular anisotropy Co/Pd multilayer upon hydrogenation

We have studied the change in saturation magnetization ($M_{S})$ and effective perpendicular anisotropy ($K_{eff}$ ) upon hydrogenation at room temperature and a pressure of one atmosphere in (Co/Pd)$_{25}$ multilayers, with Co thickness \textit{$\le $ }5 {\AA} and Pd thickness ranging from 0 {\AA} to 25 {\AA}. The change in $M_{S}$ and $K_{eff}$ was studied as a function of the x-ray scattering length density profile, generated from the x-ray reflectivity fits. The results show that when the Pd thickness \textit{$\le $ }10 {\AA}, the films were highly interdiffused, resulting in no measurable change in $M_{S}$ and $K_{eff}$ . As the thickness of Pd increases, the contrast between the Co and Pd layers increases, leading to a decrease in $M_{S}$ and an increase in the component of magnetization in the plane of the samples and hence causing $K_{eff}$ to decrease. The results clearly demonstrate that the solubility of hydrogen in the multilayer samples decreases with increasing alloying effects as it decreases the vacancy in the Pd 4$d $band leading to no electronic transfer from the hydrogen atoms to the Pd.