Cold Opto-Magnetism for Random Access Devices

Informations projet

COMRAD

N° de convention de subvention: 861300

DOI

10.3030/861300

Projet clôturé

Date de signature de la CE 12 Mai 2020

Date de début 1 Juin 2020

Date de fin 30 Novembre 2024

Financé au titre de

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Coût total

€ 3 776 243,40

Contribution de l’UE

€ 3 776 243,40

Coordonné par

STICHTING RADBOUD UNIVERSITEIT
Netherlands

Periodic Reporting for period 2 - COMRAD (Cold Opto-Magnetism for Random Access Devices)

Période du rapport: 2022-06-01 au 2024-11-30

Résumé du contexte et des objectifs généraux du projet

The ability to switch magnets between two stable bit states with the help of a magnetic field is the main principle of modern data storage technology. The move to wireless devices and the increase of cloud storage in the 21st century’s digital economy demands for even denser, faster and more energy efficient data storage. However, the heat produced by modern data centres is already a serious limitation to further increase their performance. Data centres presently consume 7% of the world electricity production, with an annual increase of 7%. It is not clear how to improve this situation which in future might contribute greatly to global warming and energy crisis. Within equilibrium thermodynamics, ultrafast magnetization reversal and least dissipative magnetic switching appear to be mutually exclusive processes. Moreover, it seems that the technology of spin switching with the help of magnetic fields is approaching its fundamental as well as practical limits, and it has been realized that even conventional magnetic-field-free, rotation-free magnetic random access memory can be much more energy efficient than hard-drives. Therefore, the demands of our digital society urge to search for new routes to control the magnetization beyond the limitations of equilibrium thermodynamics and by means other than magnetic fields. The ambition of COMRAD is to discover, explore and employ these “non- thermodynamic” routes in order to achieve the fastest possible as well as least dissipative magnetic switching leading to the ‘greenest’ random access devices.

The key objectives of COMRAD are therefore:

- Train a new generation of scientists and ambassadors of science in commerce.

- Use the knowledge of ultrafast magnetism and spintronics to develop “low dissipation sub100 ps spin-orbitronics”.

- Initiate developments of devices, such as unprecedentedly fast (THz) energy efficient magnetic memory and fs scanning probe microscopes.

At the end of the action,
- 15 ESRs have received a training from the action. All the trained ESRs are planning to continue they career either in academia or research related industry.
- The action has already resulted in 50 publications practically reporting about research towards the goals of the project.
- The action has also initiated developments of novel devices and scanning microscopes.

Travail effectué depuis le début du projet jusqu’à la fin de la période considérée dans le rapport et principaux résultats atteints jusqu’à présent

- New unique experimental facility for ultrafast spectroscopy in unprecedentedly broad spectral range (from THz to UV) with subwavelength spatial and subpicosecond temporal resolution has been developed. The facility enables to pump various electronic, phononic or magnonic transitions and identify those that have the strongest effect on spin-orbit interaction and eventually on electron spin (ESR1,2,3,5a,5b,10,13).
- Computational programs for multiscale modelling of ultrafast laser-induced spin dynamics under action of magnetic field. electric field and/or current have been developed. These program enables to explore magnetization reversal, greatly helped interpretation of experimental results obtained within the project and thus to identify the routes allowing the fastest and the least dissipative magnetic switching (ESR 6,7,11,14).
- Ultra-thin Bi-YIG films of various compositions were grown with pulsed laser deposition (PLD) and optimized to stabilize dense arrays of magnetic bubbles (ESR12).
- Magnet Tunnel Junction (MTJ) elements with integrated optical transparent electrodes have been fabricated (ESR8,9,10)
- Layer thicknesses for a Tb/Co synthetic ferrimagnet to achieve single shot switching at the smallest fluence have been optimized and led to a strong progress in realization of optically switchable Magnetic Tunnel Junctions (ESR8,9,10)
- High quality photo-switches for picosecond switching and read-out of magnetic states by electrical means were fabricated and tested.
- Various regimes of ultrafast laser-induced writing of magnetic bits as a function of applied electric and magnetic fields have been studied experimentally and computationally. Similar experiments with electric current have been also performed. ulti-dimensional parameter diagrams of the efficiency of magnetic switching on many other parameters characterizing the studied sample (film thickness, composition etc) and optical excitation (pulse duration) (ESR 6,7,11,14).
- We developed a concept of a scanning microscope allowing to reveal picosecond dynamics of the laser-induced magnetic pattern probing the latter with 100 nm spatial resolution (ESR2).
- We explored the ways to perform electrical failure analysis of nowadays semiconducting and future spin-orbitronic devices (ESR2).
- Approaches to combine the least dissipative magnetization switching with sub-100 ps (20 ps) electrical read-out have been explored (ESR2,3,4,5a,5b,6,7,8,9,10,11,13,14)
- The consortium studied on-chip magnetic switching initiated by a picosecond pulse of electric current with a picosecond read-out of the magnetic state (ESR3,4)
- We have studied the possibilities to fabricate and demonstrate an optically driven MRAM chip with the switching faster than 30 ps and heat dissipations below 10 fJ per bit (scaled to 20×20×10 nm3 bit) (ESR8,10)

Progrès au-delà de l’état des connaissances et impact potentiel prévu (y compris l’impact socio-économique et les conséquences sociétales plus larges du projet jusqu’à présent)

Progress beyond the state-of-the-art:
- Helicity-independent all-optical toggle switching of 100 nm patterned [Tb/Co] magnetic tunnel junctions (MTJ) devices, with TMR ratio exceeding 74% has been demonstrated. This is the highest reported TMR ratio so far reported in all-optical switching devices
- Switching speeds below 30 ps have been achieved using 50 fs laser pulses. An approximate absorbed energy during switching , when scaled down to scaling to a 20×20×10 nm³, was found to be as low as 10 femtojoules (fJ). It was found, however that even in ultrafast all-optical switching the minimum dissipated energy and the time of switching are mutually competing processes
- A proof-of-concept of a scanning table top Magnetic Force Microscope allowing to reveal processes of ultrafast spin dynamics with ps temporal and 100 nm spatial resolution has been demonstrated .

In the action, we have made a significant progress in demonstrating ultrafast all-optical switching of nanometre size bits with timescales below 30 ps and with energy dissipations below few tens of femtojoules. Realizing a technology based on the demonstrated effect may lead to the ‘greenest’ random access devices


Unexpectedly, a substantial socio-economic impact of this action seems to be in the development of ideas for the novel Multiplex Spectral Imaging for Chip failure Analysis. If successful, it will have substantial effects on economy and society. With accelerated lifetime tests within and beyond the product’s mission profile and analyzing the root causes of component failures, semiconductor manufacturers can understand the weaknesses or defects in design, material use, and manufacturing. Improving failure analysis in the semiconductor industry not only enhances product reliability and safety but also contributes to broader societal benefits, including sustainability, health, economic growth, and national security.

Major publications:
Phys. Rev. Applied, 20, 034070 (2023).
Nature Communications 15, 4451 (2024).
Nature Communications 14, 50000 (2024).

Wide training events/conferences:
Future Spintronics: challenging the limits (Barcelona, 2024).
Ultrafast Magnetism Conference (UMC-2022, Nancy)
Ultrafast Antiferromagnetic Writing (2022, Ingelheim)

Cartoon of a sample architecture showing local arrangementss of agnetization and the resonance exci