The origin of perpendicular anisotropy in Co/Pd multilayers has been investigated. We examined this question by studying multilayers in which the total equivalent thicknesses of Co and Pd are kept constant, but in which the Co/Pd interface is progressively alloyed using codeposition of the two elements. The multilayers have the structure: [(0.3 nm Co codeposited with y nm Pd)/(2.0−y) nm Pd]15, with y = 0, 0.1, 0.3, 0.5, 1, 1.5, 2.0. X-ray diffraction confirms that the total thicknesses of the samples and their overall Co/Pd ratios stay constant. Magnetic properties are almost unaffected by alloying up to y = 0.5 nm, suggesting that the interface of the usual Co/Pd multilayer could be modeled by a mix of 0.3 nm of Co with 0.5 nm of Pd embedded between 2 monolayers of Pd. Using this model and reasonable assumptions about the strain and magnetostriction of a Co-Pd alloy, we show that the magnetoelastic effect yields a perpendicular anisotropy between 2.3×105 and 3.5×105 J/m3. The perpendicular anisotropy estimated in our samples (1.5×105 J/m3) can thus be satisfactorily explained. © 2003 American Institute of Physics.