W. Kuch1, F. Offi2, L. I. Chelaru 2, J. Wang2, K. Fukumoto1, M. Kotsugi2, J. Kirschner2, and J. Kunes3
1Freie Universitaet Berlin, Institut fuer Experimentalphysik,Arnimallee 14, D-14195 Berlin, Germany
2Max-Planck-Institut fuer Mikrostrukturphysik, Weinberg 2, D–06120 Halle, Germany
3 Universitaet Augsburg, Institut fuer Physik, Theoretische PhysikIII, D-86135 Augsburg, Germany
For a fundamental understanding of the magnetic coupling between an antiferromagnetic (AF) and a ferromagnetic (FM) film the use of single-crystalline films with well-characterized interfaces is important. In AF materials the direction of the atomic magnetic moments varies on the length scale of atomic distances, leading to zero net magnetization if averaged over a few lattice constants. Atomic-scale control and characterization of the AF-FM interface is thus essential for a fundamental understanding of the magnetic interaction between AF and FM materials.
We present an x-ray magnetic circular (XMCD) and linear dichroism (XMLD) photoelectron emission microscopy (PEEM) study of single-crystalline bilayers and trilayers containing FeMn as antiferromagnetic layer on a Cu(001) single crystal surface. All systems show pronounced layer-by-layer growth, as confirmed by medium energy electron scattering during evaporation and scanning tunnelling microscopy. This layer-by-layer growth provides the opportunity to controllably tune the interface roughness on the atomic scale by changing the atomic layer filling. Layer-resolved XMCD-PEEM magnetic domain images reveal an oscillatory magnetic interlayer coupling between two ferromagnetic layers across an antiferromagnetic FeMn spacer layer, as well as a modulation of the phase of this oscillation and the coupling strength as a function of the bottom interface roughness.
This proves the importance not only of the presence of atomic steps at the interface, but also of their detailed arrangement. Because of the three-dimensional non-collinear spin structure of FeMn films, the XMLD signal of the AF layer vanishes. However, it was possible to identify the tiny XMLD signal of the induced moments in the FeMn layer at the interface. These are the first magnetic domain images of a metallic AF acquired with XMLD. Interestingly, also the XMLD signal of the FM layer is influenced by the contact to the AF layer.
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