In ultrathin magnetic films deposited on heavy elements substrates, the interface-induced Dzyaloshinkii-Moriya interaction allows to stabilize non-collinear spin structures like magnetic skyrmions. These topologically protected objects are interesting for future data storage technologies like racetrack memories.
We present spin-polarized scanning tunneling microscopy investigations on a three-atomic-layer thick Fe film deposited on Ir(111). In this system, the large epitaxial strain is relieved by the formation of a dense dislocation lines network. This particular structure of the film induces a symmetry breaking with dramatic consequences on the magnetic state. In zero field, spin spirals propagate along the dislocations lines and their period depends on the spacing between these lines, i.e. on the strain relief, which is locally varying . We attribute this effect on the spirals to modifications of the exchange coupling.
Single skyrmions appear in external magnetic field. We demonstrate that they can reliably be written and deleted by an STM tip . The strong-bias polarity dependence and the linear behavior of the threshold voltage for switching with the tip-sample distance shows that electric field plays the dominant role in the switching mechanism. This switching between the topologically distinct magnetic states by electric fields may be beneficial in future spintronic devices employing skyrmions as information carriers.
We acknowledge financial support by the European Union via the Horizon 2020 research and innovation program under Grant No.665095.
 Finco et al, PRB 94, 214402 (2016)
 Hsu et al, Nat. Nanotech. (2016)