Bi/Mn/Al/Bi/Mn multilayers with different Al‐interlayer thickness have been deposited on glass substrates at room temperature. The multilayers are not protected by a passivating layer, such as SiOx, in order to investigate the interplay between Al‐interlayer thickness and homogeneity, granularity, and topography before and after annealing. Due to the Al interlayer, the diffusion across the Bi/Mn/Al/Bi/Mn stack was reduced as demonstrated by x‐ray analysis, scanning electron microscopy, and Rutherford backscattering spectrometry. During annealing, two (MnxBi100−x)100−yAlylayers are formed which are separated by an Al interlayer. After annealing, polar Kerr hysteresis loops as measured from the front side of the films show a superposition of two hysteresis loops, opposite in sign, with different coercive fields. The presence of different coercive fields is explained by different granularity of the top and bottom (MnxBi100−x)100−yAlylayer. The coercive field of the top (MnxBi100−x)100−yAlylayer reaches values up to 1.25 T, while the bottom layer shows a constant value of 0.3 T independent of the Al‐interlayer thickness. The opposite sign of the two contributions to the Kerr loops is explained by the different relative index of refraction at the air/(MnxBi100−x)100−yAlyand the Al/(MnxBi100−x)100−yAlyinterface. ©1996 American Institute of Physics.