Determination of the ferromagnetic coupling across Pd by magneto-atomic engineering

The ferromagnetic coupling across Pd interlayers has been determined from hysteresis loop measurements on perpendicular-magnetized multilayers of the type M₃/8 Ru/M₂/xPd/M₁. Here M₁, M ₂, and M₃ denote magnetic layers consisting of (strongly ferromagnetically coupled) Co/Pd multilayers with perpendicular magnetic anisotropy: M₁=[3Co+4×(4Co+6Pd)], M₂= [3Co+4×(4Co+6Pd)+7Co] and M₃=[20×(6Pd+4Co)+3Co]. (The layer thicknesses are in Å.) The determination of the ferromagnetic coupling across the Pd interlayer with variable thickness x was enabled by pinning the second magnetic layer M₂. This pinning was achieved by the relatively strong antiferromagnetic coupling (by the Ru layer) to the thickest magnetic layer M₃. The hysteresis loops displayed a staircase behavior, with two or three steps (levels), depending on the strength of the ferromagnetic coupling. From the fields at which the steps occurred, the ferromagnetic coupling across Pd, as well as the antiferromagnetic coupling across the 8 Å Ru layer, were determined. A monotonic decrease of the former was observed from 0.17 mJ/m² at 14 Å Pd to ≊0.02 mJ/m² at 20 Å Pd.