The effect of a ferromagnetic Gd marker layer on the effective work function (WFeffFe) of Fe in a Fe/ Gd/Al2O3/Si stack has been systematically investigated by hard X-ray photoelectron spectroscopy (HAXPES) and capacitance-voltage measurements. A pronounced change in the band alignment at the buried Fe/Al2O3 interface WFeffFe=4.5/3.7eV is revealed by HAXPES as a function of the Gd marker thickness in the range 0/2.7 nm, in agreement with capacitance-voltage (C-V) data. Interface-sensitive 57Fe conversion-electron Mößbauer spectroscopy performed on Fe/Gd/Al2O3/Si stacks reveals major structural and magnetic changes at the Fe/Gd interface for different Gd thickness, which are correlated with the changes of the Fe/Al2O3 band alignment.