On the perpendicular anisotropy of Co/Pd multilayers

The two principal mechanisms for explaining the perpendicular anisotropy in Co-Pd multilayers were investigated. These mechanisms are the broken symmetry at sharp Co surfaces, and the magnetostriction of interfacial Co-Pd alloys under stress due to epitaxy with Pd. The approach was to examine multilayers in which the Co component was intentionally alloyed with different amounts of the Pd, keeping the total amount of Co and Pd constant. These multilayers were deposited both at room temperature, at which thermally activated interfacial intermixing augmented the intentional alloying, and at 77 K where sharper interfaces reflecting the intentional alloying were expected. Comparison of the properties of these two sets of multilayers clearly indicated that stressed interfacial alloying is the dominant mechanism. Low-temperature measurements supported the alloying model, and the presence of polarized Pd. Furthermore, the hard-axis magnetization was modeled with a distribution of local perpendicular anisotropies which reflect local composition variations.