INSP - UPMC - 4 place Jussieu - 75005 Paris - Barre 22-32, 2e étage, salle 201
Alexandra Palacios - Post-doc à Karlsruhe dans le groupe du Prof. Wiesendanger
Recently, there has been increasing interest in non-collinear magnetic states in ultrathin films and several complex spin textures have been reported . Typically such non-collinear spin configurations arise due to competing interactions, for instance nearest neighbor and next-nearest neighbor Heisenberg exchange, which can lead to spin spirals with a period given by the ratio of the interaction strengths. The magnetic interactions of a thin-film system are governed by the distance and the number of nearest neighbors, by the adsorption geometry, and the hybridization with the non-magnetic substrate. For Fe thin films it has been demonstrated that not only different substrates [2-3] but also a different stacking, uniaxial strain relief, or different symmetry of a surface can lead to a variety of magnetic ground states [1, 4-5]. This suggests that different non-collinear magnetic ground states may coexist, giving rise to the question about mutual interactions between them. Here, we report on spin-polarized scanning tunneling microscopy (SP-STM) measurements of an Fe monolayer on Re(0001). In addition to the previously observed Néel state in the pseudomorphic hcp-stacked Fe monolayer , we find a spin spiral state in dislocation lines that are incorporated to release lateral strain. A close analysis reveals that within a dislocation line the spins are canted with respect to the dislocation line propagation. At the interface between these two coexisting non-collinear magnetic states we find a sharp transition on the order of a few atoms only. In addition, a spatial correlation between the spin spiral and the Néel state suggests a coupling between the two states, which is confirmed by Monte-Carlo simulations 
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