Room temperature stabilization and all-electrical manipulation of chiral spin structures in metallic multilayers

Project Information

SKDWONTRACK

Grant agreement ID: 748006

DOI

10.3030/748006

Project closed

EC signature date 28 February 2017

Start date 1 January 2018

End date 31 December 2020

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 239 860,80

EU contribution

€ 239 860,80

Coordinated by

UNIVERSITY OF HAMBURG
Germany

Periodic Reporting for period 2 - SKDWONTRACK (Room temperature stabilization and all-electrical manipulation of chiral spin structures in metallic multilayers)

Reporting period: 2020-01-01 to 2020-12-31

Summary of the context and overall objectives of the project

The upcoming revolution in information technology driven by the internet-of-things, artificial intelligence and quantum computing will require a change in the way we generate, store and process information.
On the one hand, the development of new systems with embedded intelligence and sensing devices (like in autonomous driving cars) will generate a massive increase in computation. This will not be feasible at current levels of devices’ power consumption, which calls for the design of more energy efficient technologies. While semiconductor microelectronics has reached its intrinsic limitations, spintronics offers a new path towards the design of memory and logic devices with high density and low power consumption. However, present spintronic devices such as magnetic-RAMs still suffer from high current density requirements. These drawbacks call for the development of new magnetic materials systems with intrinsically stable magnetic states, easy to manipulate and detect at a low energy cost. Metallic multilayers hosting non-collinear spin-structures such as magnetic skyrmions offer a highly promising solution. Their topological stability and outstanding transport properties make them a natural choice for the development of new memory and logic devices.
On the other hand, in the last 15 years quantum computing moved from being a mere theoretical subject to a more applied one. Currently, there is a large interest in the discovery and development of new quantum materials which can be employed in the design of quantum computers. Non-collinear magnetic systems (e.g. skyrmionic systems) can play an important role in the development of new quantum materials. Indeed, the combination of superconducting materials and non-collinear magnetic systems can give access to what is called topological superconductivity, which is very interesting for the development of quantum computing systems.
The main objective of the project was the design, investigation and engineering of new metallic multilayers hosting non-collinear and topologically protected magnetic states. Several different materials systems hosting non-collinear magnetism have been developed and studied. One main achievement of the action was the stabilization and the tuning of room-temperature magnetic skyrmions in the absence of any external magnetic field. This is key to the design of skyrmion-based electronic devices which are compatible with the miniaturization requirements of nanoelectronics.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

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)

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Our demonstration of the tuning of room temperature zero-field magnetic skyrmions via interlayer magnetic coupling represents one more step towards the development of skyrmionic systems applicable in low power spintronic devices. Indeed, it is now possible to study the transport properties of zero-field skyrmions, a key ingredient in the design of new, low-power magnetic data storage devices. This could play a major role in the reduction of the energy requirements, and so of the carbon footprint, of large computational systems and data centers around the world.
In addition to the possible application of skyrmions in spintronic devices, topological magnetic spin-textures can also be employed in the making of new quantum materials systems. Indeed, joining non-collinear magnetism (e.g. skyrmions) and superconductors can give access to topological superconductivity, which can be applied in topological quantum computing. Accordingly, the development of a platform where magnetic skymions can be stabilized without any external magnetic field offers a new way towards the design of quantum technologies.

Figure 1: Stabilization of zero-field magnetic skyrmions via interlayer magnetic coupling.