Fe/Nb/Fe trilayers were prepared at room temperature using UHV magnetron sputtering. The interlayer exchange coupling energy was determined from a shift of the minor hysteresis loop from the origin. Results showed clear antiferromagnetic (AF) coupling maxima near ~ 6 and 9 monolayers of Nb spacer. Calculations of the interlayer exchange coupling energy were carried out using ab-initio method with localized spin density approximations of exchange-correlation potential. The experimental results were in good agreement with ab-initio calculations. Furthermore, the position of the AF peaks and coupling energy values could be modified using hydrogen. [ABSTRACT FROM AUTHOR]