Topological properties of magnetic skyrmions and opportunities for novel spintronic devices – TOPSKY

To complete the ambitious perspective of TOPSKY, a smart and optimized engineering of the material and interfacial properties will be undoubtedly required. It will then be essential to get a deeper understanding of the transport and dynamical properties of ultra-small magnetic skyrmions. Although they are key issues from the viewpoints of both fundamental science and applications, they have only been scarcely addressed up to now, notably with skyrmions at room temperature. We ambition to make the bridge between the fundamental properties of skyrmions (WP1) and applications (WP2). Consequently, we have identified five scientific knowledge gaps that will be extensively addressed in the work program of TOPSKY:
1 - Reduction of skyrmion size and control of their interaction with defects.
2 - Mechanisms for nucleation and/or annihilation of skyrmions.
3 - Coupling between conduction electrons and skyrmionic spin textures.
4 - Spin transfer induced motion of skyrmions.
5 - Dynamics of skyrmionic textures.
These advances defined as the scientific objectives of the first work package “Investigation and optimisation of skyrmion properties” should then allow us to achieve a better control of the generation, the manipulation, the excitation and the detection of ultra-small skyrmions in MML systems. These are compulsory technical objectives as they correspond to the basic functions needed for any type of skyrmion based devices such as memory, radiofrequency or logic devices, as the ones that will be designed, fabricated and evaluated in the second work package of TOPSKY project entitled “Toward skyrmion based devices”.

See publication list.

The project is well underway, with the stabilization of small skyrmions in various systems.

1. A. Hrabec et al, Phys. Rev. Lett. 120, 227204 (2018)
2. W. Akhtar et al, Phys. Rev. Appl. 11, 034066 (2019)
3. J. Miltat et al, Phys. Rev. B 97, 214426 (2018)
4. W. Legrand et al, Phys. Rev. Appl. 10, 064042 (2018)
5. D. de Souza Chaves et al, Phys. Rev. B 99, 144404 (2019)
6. L. Desplats et al, arXiv:1902.09915, à paraître dans Phys. Rev. B (2019)

Challenges facing nano-technology for power efficient, high density, high speed information processing and storage are well recognized and known as the approaching end of Moore’s law. In fact, strategies for meeting them in the short term define the shape of roadmaps for the electronic industry. However, it is anticipated that alternative solutions will have to be experimented and some of them eventually implemented in order to tackle these different challenges.
The objective of TOPSKY project is to investigate and validate one of these alternative approaches based on the use of magnetic skyrmions to deeply transform the way, data can be stored and manipulated. The paradigm here relies on their topological character which makes them suitable for “abacus”-type applications in information storage or logic technologies.

The investigation of magnetic skyrmion properties has become an extremely hot topic in condensed matter physics in the last couple of years. Several reasons explain this “passion” for skyrmions. First, because of their topological nature, they are, or should be, stable against any transition towards another magnetic configuration leading to the fact that they are supposed to exhibit a reduced influence against defects (even though recent studies suggest a significant impact of pinning on defects). Another advantage due to topology is that they can be stable even with a size down to a few nanometers, and are thus considered as the ultimate candidate for magnetic data storage in magnetic films. Finally, as it was demonstrated already in 2010, they can be moved at extremely low current densities through spin transfer torques. Soon after these observations, mostly realised in bulk non centro-symmetric materials, it was proposed to leverage on these fascinating properties of magnetic skyrmions to define a world of opportunities for a new generation of spintronic devices for various ICT applications. However, having these perspectives in mind, a crucial step was missing: the demonstration that these magnetic skyrmions can exist at room temperature and low (or even zero) field in materials industrially relevant. This key achievement has been reached in 2015, simultaneously by a few groups in the world (two of them being part of TOPSKY), showing that skyrmions with sizes around 100 nm can be imaged at room temperature in thin magnetic multilayers with large interfacial chiral interaction such as Pt/Co/Ir, Pt/Co/Ta or Pt/Co/MgO.

In TOPSKY, we will proceed with this strategy and focus our effort, as described in the work program, on the identification and the extensive characterization of novel optimized systems made from different types of magnetic multilayers, enabling the observation and the use of skyrmions that have much smaller sizes and are more mobile compared to the state-of-the art. Beyond the new scientific breakthroughs concerning the skyrmion physics that we expect to obtain with our research, the main technical objective in TOPSKY aims at contributing to a potential revolution in ICT in bringing these fascinating topological magnetic objects into a new generation of room temperature topological-electronic devices. The ambition is indeed to devise and fabricate proof-of-concept skyrmion based devices that range from still highly silicon-compatible memories, such as multi-level MRAMs or even skyrmion racetrack memories to disruptive “beyond CMOS” technologies such as neuro-inspired architectures. We believe that this is unique opportunity to make the bridge between the topological phenomena and the demonstration of some basic functions for future nanodevices.