Magnetic coupling in Co/face-centered-cubic Fe/Co sandwiches

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Abstract
Ferromagnetic (FC) and antiferromagnetic coupling (AFC) of Co layers across a metastable fcc Fe spacer layer has been observed. Room‐temperature‐grown Fe on Co/Cu(100) was chosen as a spacer layer because it exhibits three distinct structural and magnetic phases depending on the thickness range: fct and ferromagnetic (region I), fcc and nonferromagnetic (region II), bcc and ferromagnetic (region III) (listed in order of increasing thickness). Co/Fe/Co sandwiches were grown on Cu(100) by molecular beam epitaxy with a base pressure of ∼2×10−10 Torr, and characterized by low‐energy electron diffraction and reflection high‐energy electron diffraction. The magnetic properties were studied in situ using surface magneto‐optic Kerr effect. Using a wedged Fe spacer layer, we investigated the magnetic coupling between Co films across many thicknesses of Fe. We found FC in region I, strong AFC at the boundary between regions I and II, and weak AFC in region II. We also studied the effect of just the Co overlayer on the metastable fcc Fe. We find that Co/Fe/Cu(100) differs qualitatively from Fe/Co/Cu(100). Finally, we find an oscillation in the AFC with a periodicity of ∼12 Å by artificially increasing the thickness range of region II.