Spintronics, which manipulates electron spin, has the potential to accelerate the speed and reduce the energy consumption of electronic devices. However, generating and manipulating spin textures in materials remains a challenge. A recent Spanish-German research team discovered that when graphene is layered with heavy metals such as cobalt and iridium, it exhibits enhanced quantum effects, such as increased spin-orbit coupling and spin canting, which is highly beneficial for the development of spintronics.
Table of Contents
Graphene and Spintronics
Spintronics utilizes the spin of electrons to perform logic operations and data storage. Spintronic devices have the potential to surpass traditional semiconductors in terms of speed and energy efficiency. However, generating and manipulating spin textures within materials poses significant challenges. Graphene, a two-dimensional honeycomb structure composed of carbon atoms, is considered a potential candidate material for spintronic applications. When graphene is deposited on a thin film of heavy metal, it generates strong spin-orbit coupling at the interface, leading to various quantum effects, including the Rashba effect (spin-orbit splitting of energy levels) and the Dzyaloshinskii-Moriya interaction (tilting of spin alignment). In particular, the spin canting effect can be used to stabilize vortex-like spin textures (skyrmions), which are considered key elements for future spintronic devices.
※Knowledge Supplement: Spin is a property of electrons that can generate magnetism and influence electronic component applications. Unlike traditional electronic components, spin control offers more possibilities. When magnetic and non-magnetic materials come into contact, they interact and produce the “magnetic proximity effect,” a property widely used in magnetic memory.
Enhancement by the Cobalt Layer
The Spanish and German research team recently found that when a single layer of the ferromagnetic element cobalt is inserted between graphene and a heavy metal (such as iridium), these quantum effects are significantly enhanced. The team grew samples on an insulating substrate to ensure that these effects could be effectively applied in multifunctional spintronic devices.
Spectroscopic analysis conducted at the Helmholtz-Zentrum Berlin (HZB) BESSY II showed that graphene interacts not only with the cobalt layer but also indirectly with the iridium layer through the cobalt. This means that the interaction between graphene and the heavy metal is mediated by the ferromagnetic cobalt layer, which enhances the splitting of energy levels and the spin canting effect.
Breakthrough Experimental and Theoretical Verification
Dr. Jaime Sánchez-Barriga, a physicist at HZB, pointed out that the spin canting effect can be influenced by adjusting the number of cobalt monolayers, with three cobalt monolayers showing the best results. This result was supported by both experimental data and density functional theory (DFT) calculations. The mutual influence and enhancement of the two quantum effects is a key and unexpected finding of this research.
This breakthrough was made possible by the advanced spin- and angle-resolved photoemission spectroscopy (Spin-ARPES) technique at BESSY II. Sánchez-Barriga stated that this technique allowed the research team to precisely measure the spin canting effect and Rashba-type spin-orbit splitting in the material, even resolving its derivative, which can be more significant than the electron spin itself.
Only a very small number of institutions worldwide possess measurement equipment with such high sensitivity. Therefore, the results of this research lay a solid foundation for the application of graphene-based heterostructures in next-generation spintronic devices, demonstrating their immense potential. Further exploration of different combinations of ferromagnetic layers or heavy metals may lead to the discovery of more novel quantum effects, accelerating the practical application of spintronic technology.
Reference
- Spintronics Breakthrough: Inserting Cobalt Layer Unleashes Graphene’s Quantum Potential
- Spintronics Breakthrough: Unlocking the Quantum Potential of Graphene With Cobalt
- Beatriz Muñiz Cano, Adrián Gudín, Jaime Sánchez-Barriga, Oliver Clark, Alberto Anadón, Jose Manuel Díez, …Paolo Perna (2024). Rashba-like Spin Textures in Graphene Promoted by Ferromagnet-Mediated Electronic Hybridization with a Heavy Metal, ACS Nano, Vol18, Issue24, DOI: 10.1021/acsnano.4c02154
(Source of first picture: Dall-E/arö/Helmholtz-Zentrum Berlin)
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