The groundbreaking idea at the core of the MAGicSky proposal was to use the magnetic nanoscale quasi-particle that are the magnetic skyrmions and their exceptional properties, most of them associated to their topological nature, as a support of information in a new generation of spintronic devices. Predicted about 30 years ago, a skyrmion lattice phase was observed only 20 years later at low temperature and under large magnetic fields in non-centro-symmetric magnetic crystals such as MnSi of CoFeGe and using experimental techniques such as small angle neutron scattering or Lorentz TEM. Neither the compounds that were investigated not the experiments used to characterize them were not adapted with any kind of applications. The strategy adopted in MAGicSky to rely on skyrmions stabilized at room temperature in thin films and multilayers compatible which are compatible with industrial process on a long term took its infancy with the pioneer works realized by UHAM partner a few years before MAGicSky demonstrating that skyrmions stabilized by a large interfacial DM interaction can be very small with diameters in the nm range. Based on this discovery, we proposed to develop a complementary approach mixing model epitaxial systems with sputtered grown samples together with a strong theoretical support first to reach room temperature (RT) stabilization. Then, our second big objective was, because skyrmions behave as quasi-particles that can be moved by spin transfer torques, be created or annihilated, to rely on all these remarkable properties, that by the way were almost not studied yet in thin films and multilayers, to make them suitable for “abacus”-type applications in information storage devices, logic technologies and more recently for magnonic and neuromorphic hardware nanodevices.
One of our strategic choices in MAGicSky is to tailor the interface-DM interaction to observe by different imaging techniques some isolated skyrmions at RT in magnetic multilayers (MML) by stacking ultra-thin layers of transition metals (Co, Fe) and spin-orbit metals (Pt, Ir, W, Rh…) alternately. The concerted effort made during the first period enabled us to achieve this first challenging objective with the observation by several imaging techniques (STXM, MFM) and on different MML systems such as Pt/Co/Ir or Pt/Co/AlOx multilayers, some magnetic skyrmions at RT. This key advance has generated a large interest and was crucial for the success of MAGicSky as it was a prerequisite for the addressing the other fundamental objectives. Beyond this achievement, a lot of efforts combining experimental results in epitaxial MML systems and theoretical calculations by e.g. first principle calculations, spin dynamics and Monte Carlo simulations have been performed in the second reporting period to evaluate how the important magnetic parameters can be tuned by changing materials and composition to improve and optimize the skyrmion characteristics. One important challenge was notably to better understand and improve their thermal stability while decreasing their size. To this aim, we rely on elaborating samples with multiple repetitions instead of single thin films. The prize to pay for that is that the interlayer dipolar fields then become more important and can strongly modified the skyrmion shape and size. A combination of experiments, numerical simulations and modelling have been done during this period to tackle this issue, for example with the identification of hybrid chiral skyrmions in some cases, and proposed some guidance for the choice of magnetic parameters to eventually obtain ultra-small and mobile skyrmions at RT. Another important issue has been to improve understanding the interaction with defects or pinning centers.
