- The paper demonstrates that significant Dzyaloshinskii-Moriya interaction, reaching up to 1.14 meV/atom, is induced at graphene/ferromagnet interfaces through the Rashba effect.
- It employs first-principles calculations and band structure analysis to quantify the Rashba splitting and validate the DMI strength.
- Experimental SPLEEM observations reveal a transition from chiral Néel to achiral Bloch walls, underscoring potential for advanced spintronic devices.
Significant Dzyaloshinskii-Moriya Interaction at Graphene-Ferromagnet Interfaces due to Rashba-effect
The paper presented provides valuable insights into the unexpected spintronic properties of graphene when interfaced with ferromagnetic metals such as cobalt (Co) and nickel (Ni). Traditionally, graphene is considered a weak spin-orbit coupling material, yet it demonstrates significant potential in spin orbitronics through the induction of chiral spin textures at the graphene/ferromagnet (FM) interface. This capability is attributed to a unique Dzyaloshinskii-Moriya Interaction (DMI) facilitated by the Rashba effect.
Graphene's Role in Spintronic Phenomena
Graphene, notable for its unique electronic properties, including long spin diffusion length and pronounced magnetic phenomena such as tunnel magnetoresistance and quantum spin Hall effect, becomes a critical player in enhancing spintronic applications. Despite limited intrinsic spin-orbit interactions, graphene significantly impacts DMI due to the Rashba effect. In this paper, graphene interfaces with Co and Ni are explored for their ability to generate pronounced DMI, comparable to interfaces with heavy metals typically known for substantial spin-orbit coupling.
Computational and Experimental Analysis
First-Principles Calculations
The researchers employed first-principles calculations to model graphene/Ferromagnet (FM) multilayer structures. The computational results reveal that the DMI magnitude at the graphene/Co interface can reach up to 1.14 meV per atom for a monolayer and decreases for thicker multilayers. Interestingly, the Rashba-type DMI dominates over Fert-Levy model predictions, with the largest spin-orbit energy variation occurring at the interfacial Co layer.
To further validate these findings, the authors calculated the Rashba splitting and derived the DMI value from band structure analyses. Their findings align well with the first-principles calculations, confirming the influence of the Rashba effect in driving the DMI at the graphene/FM interface.
Spin-polarized Low-Energy Electron Microscopy (SPLEEM)
Experimental confirmation of the predicted DMI was achieved through SPLEEM, allowing visualization of the domain wall (DW) structures in graphene-coated FM films. The experimental results indicated a transition from chiral Néel walls to achiral Bloch walls as FM layer thickness increased, consistent with the calculated DMI trends. This transition serves as an indirect method to quantify the DMI strength.
Implications and Future Directions
The presence of significant DMI at graphene/FM interfaces opens several avenues for future research and technological development. The observed Rashba-effect-induced DMI suggests possibilities for engineering chiral spin textures in two-dimensional materials, potentially leading to the creation of ultra-compact spintronic devices.
Moreover, given the tunable nature of the DMI in graphene-based heterostructures, there is a practical potential for further enhancing DMI values through structures like graphene/[Co/Ni] superlattices. Such enhancements can, in turn, facilitate the stabilization of skyrmions and other chiral magnetic phenomena, crucial for advanced memory and logic devices with reduced power consumption and increased speed.
Conclusion
This paper demonstrates that graphene can induce significant DMI, a finding crucial for developing advanced spintronic devices. By leveraging first-principles calculations and SPLEEM experiments, the authors elucidate the role of the Rashba effect in graphene-induced DMI, presenting a novel mechanism different from traditional heavy-metal interfaces. These insights not only broaden the application spectrum for graphene but also pave the way for novel spintronic technologies rooted in two-dimensional materials. Preparing these interfaces efficiently and understanding their detailed physics will be central to future developments in the field.