From a simplified quantum-well model for a magnetic sandwich, it can be shown that in the variation of the number of occupied levels with the spacer layers, there exists an intrinsic periodicity, which leads the Fermi level to oscillate periodically. The intrinsic periodicity does not depend on the magnetic alignment but only on the quantum-well states themselves. The oscillation period can be approximately given by , where and are the effective masses of the electron in the lateral and perpendicular directions respectively, is the distance between the two neighbouring atomic layers, and is the electron density in the spacer layers. This makes one speculate that the long periodicity of the oscillatory coupling could be a result of the intrinsic periodicity, if and a small s-electron density are assumed. On the other hand, from the calculated energy bands for a thin film, it is found that the electronic structure is highly anisotropic, which is in agreement with this assumption. Therefore, it can be confirmed that the intrinsic periodicity plays an important role in the oscillatory coupling. An inverse photoemission experiment on Cu(100) films over Co can be explained quite well using this physical picture.