In the present treatise magnetic and magneto-optic properties of Fe/Tb multilayers are investigated using Kerr spectroscopy, SQUID and Torque magnetometry in order to clarifiy the influence of interfaces on the magnetization reversal and the origin of the magnetic perpendicular anisotropy (PMA). The torque curves evidence different mechanisms to induce the PMA, viz., formation of alloy at rough Fe-on-Tb interfaces and antiferromagnetic coupling between Fe and Tb moments at smooth Tb-on-Fe interfaces. In addition, the observed magnetic cone structure is confirmed by model calculations based on the model due to Stoner and Wohlfarth. Different Fe modifications as isolated amorphous Fe, FeTb alloy and bulk amorphous Fe are identified on inspection of the polar Kerr curves. According to the Kerr spectra, the contribution of amorphous Fe in multilayers increases with increasing number of a-Fe/Tb bilayers.