In order to obtain a deeper insight into the inter-relation of magnetism and morphology we compare the properties of Fe films on Cu(100) and Cu3Au(100) grown at different temperatures, using the magneto-optical Kerr effect and scanning tunnelling microscopy. In Fe films on Cu3Au(100) for both room- and low-temperature growth (RT and LT growth) neither an antiferromagnetic phase nor a good layer-by-layer growth, as found for RT growth in Fe/Cu(100), was observed. The critical thickness at which the spin reorientation transition from perpendicular to in-plane easy axis starts, is found to be 3.5 ML for RT-grown Fe/Cu3Au(100) as compared with 5.5 ML for the LT-grown films on both substrates.