The initial part of the project has been characterized by the development of epitaxial magnetic multilayers on top of insulating single crystal substrates. The interest in growing metallic multilayers on top of insulating substrates lies in the possibility to explore the magneto-transport properties of the developed materials stacks, such as current-induced skyrmion motion. We successfully developed a recipe for the growth of epitaxial metallic multilayers on top of insulating MgO single crystals. Via spin-polarized low energy electron microscopy (SPLEEM) we were able to explore the type of magnetic texture stabilized in those multilayers. The investigation with the SPLEEM confirmed the presence of magnetic spin-textures with a uni-directional sense of rotation, which is a key requirement for the stabilization of magnetic skyrmions. After the establishment of multilayers hosting the desired non-collinear spin-textures, we further developed our stacks so to obtain the stabilization of magnetic skyrmions at room temperature in no external magnetic field. We exploited the interlayer magnetic coupling between two different ferromagnetic thin films separated by a non-magnetic spacer (see Fig. 1) in order to nucleate skyrmions at zero field. After their stabilization we also investigated their topological nature, revealing their handedness (right handed vs left-handed). Interestingly, by tailoring the thickness of the non-magnetic spacer we were able to fine-tune the strength of the coupling between the two magnets, which resulted in the control of the skyrmion size and areal density. The main findings of this part of the project are reported in the following publication: R. Lo Conte et al., Nano Letters 20, 4739-4747 (2020).
Furthermore, the project also focused on the understanding of new ways to stabilize non-collinear magnetism in thin film systems. Until now, due to the requirement of large spin-orbit coupling (SOC) for the stabilization of non-collinear spin-textures, [heavy metals]\magnet heterostructures have represented the main platform for this kind of studies. Accordingly, the interest was in going beyond the [heavy metal]\magnet platform and discover new mechanisms to stabilize non-collinear magnetism. In this direction goes the exploration and demonstration of the stabilization of non-collinear spin-textures in a multilayer system via Oxygen chemisorption (G. Chen, R. Lo Conte et al., Science Advances 6 : eaba4924 (2020)). This surprising effect is understood as the result of the presence of a large Rashba-SOC at the Oxygen/magnet interface, which opens up a complete new avenue for the stabilization of topologically non-trivial magnetic states in thin-film magnetic systems.
All the scientific results obtained in this project have contributed to better understand the origin of non-collinear, topological spin-textures in magnetic thin film multilayers, allowing to make one more step towards the design of novel solid state magnetic memory and logic devices based on topologically protected spin-states.
In order to maximize the impact of this action among the scientific community, the scientific results described above have been/will be presented at several national and international seminars and conferences:
1. APS March Meeting 2021 (virtual), March 2021 (invited)
2. Joint European Magnetic Symposia (JEMS) 2020 Virtual Conference, Dec 2020
3. Virtual Conference on Magnetism and Magnetic Materials 2020, Nov 2020
4. Imaging Facility Seminar, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley-CA, USA, Dec 10, 2019 (invited)
