Anomalous Perpendicular Anisotropy in Ultra-Thin Co Films

Abstract
We have used in situ polar Kerr effect measurements to study the magnetic coercivity and anisotropy of MBE-grown Pd (111) /Co/X and Au (111) /Co/X trilayers, where χ is the nonmagnetic noble or transition metal overlayer Ag, Cu or Pd. Polar hysteresis curves were Measured in situ for systematically varied Co and overlayer thicknesses 2 Å ≤ tco ≤ 20 Å and 0 Å ≤ tx ≤ 50 Å. We find the coercivity and total anisotropy display a strongly peaked perpendicular contribution at ∼1 atomic layer (2 Å) non-Magnetic Metal coverage. For Cu, where the effect is strongest, the total anisotropy energy rapidly decreases by a factor of 3 from its peak value after a total coverage of ∼2 atomic layers (4 A) of Cu.

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