Tailoring the Magnetic Coupling of Fe/Cr/Fe Trilayers by Using Substrates with Nanometer Scale Ripples

Artificial antiferromagnets made from magnetically coupled trilayer structures are the basis for all types of spintronic devices like MRAM, GMR sensors etc. For years major effort lay on adjusting the coupling strength by changing the spacer thickness or material. Today, nanostructures offer a different approach as they add additional coupling mechanisms like proximity effects or Néel orange-peel coupling to the common interlayer exchange coupling (IEC). By means of ion beam erosion techniques it is possible to create well ordered substrate ripples with nanometer periodicity. They are transferred into the films grown on these rippled substrates. Hence, such ripples are a convenient way to induce Néel orange-peel coupling [1] and thus allow for tailoring the magnetic properties [2] as well as the coupling strength by varying the ripple periodicity without adjusting the spacer thickness. We have investigated the influence of rippled vs. flat Si substrates on the interlayer exchange coupling contributions in polycrystalline Fe (4nm)/Cr (x nm)/Fe (4nm) thin film trilayers (x=0–5 nm). The substrate surface was periodically modulated (periods of 23 nm and 37 nm) by Ar+ ion beam erosion. The influence of the resulting surface and interface structure on the magnetic properties has been investigated by longitudinal magneto-optical Kerr effect (MOKE) applying a Stoner-Wohlfarth model on the magnetization reversal loops. Using 23 nm period ripples, we find an orange peel type coupling, predicted by Néel's theory superimposed on the IEC. In addition due to the morphology of the magnetic layers, a strong uniaxial magnetic anisotropy is induced.
This work is supported by DFG grant FA 314/6-1.
REFERENCES
1. Körner M. et al., Physical Review B 80, 214401, 2009.
2. Fassbender J. et al., New Journal of Physics 11, 125002, 2009