Influence of Interface Alloying on the Magnetic Properties of Co/Pd Multilayers
J Carrey, A. E. Berkowitz, William F. Egelhoff Jr., D J. Smith
An important issue concerning Co/Pd multilayers is the origin of their perpendicular anisotropy. One explanation is broken symmetry of Co atoms at the Co/Pd interface; another involves magnetoelastic effects in an interfacial Co-Pd alloy. 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 co-deposition of the two elements. The multilayers have the structure: [(Co-0.3 nm co-deposited with Pd-y nm) / Pd-(2.0-y) nm]15, with y=0, 0.1, 0.3, 0.5, 1.0, 1.5, 2.0. X-Ray diffraction data confirm that the total thicknesses of the samples and their Co/Pd ratios stay constant in the series. Magnetic properties are almost unaffected by the alloying up to y= 0.5 nm. This suggests that the interface of the usual Co/Pd multilayer could be modeled by a mix of 0.3nm of Co with 0.5 nm of Pd embedded between 2 monolayers of Pd. Such a picture of the interface is in good agreement with our magnetization data. 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 and 3.5106 erg/cm3. The perpendicular anisotropy estimated in our samples (1.5106 erg/cm3) can thus be satisfactorily explained with this model.