Novel nanomaterials for spintronics: an ab initio approach

• Applicant: Professorin Dr. Zeila Zanolli
• Subject Area: Theoretical Condensed Matter Physics
• Term: from 2016 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 313763069

The research challenges of the near and far future in electronics focus on the quest for new materials and novel device concepts to achieve low energy consumption, increased reliability and high device density. These can be obtained by designing active elements and interconnects whose operating principle is not (only) based on the electron charge but on the spin degree of freedom of the electron, i.e. developing new materials for spintronic applications. The investigation of nanoscopic materials requires atomistic parameter free (ab initio) simulations to accurately predict their properties and design new compounds.The best materials for spintronics are magnetic semiconductors with high spin-orbit coupling (SOC). Conventional inorganic semiconductors and metals suffer from short spin diffusion lengths and result in spin devices with weak spin signals. It is crucial to design novel materials for spintronic applications, which is the main goal of this Project. Magnetism has been observed at the nanoscale thanks to reduced dimensionality, unsaturated surface atoms, defects, quantum confimenent effects, and surface functionalization with magnetic molecules or metallic nanoclusters. The most promising systems include carbon-based nanomaterials (nanotubes, nanoribbons, graphene,...), magnetoelectric multiferroics, hybrid organic-inorganic nanostructures, and Transition Metal Dichalcogenides (TMD). All present interesting features and many open problems.Carbon-based nanomaterials are characterized by spin diffusion lengths of up to 100 microns and high electron velocities, which are crucial features for channel materials in spin transistors. However, a large spin diffusion length comes at the price of small SOC, which limits the possibility of manipulating electrons via an external applied field. To achieve graphene-based devices one also needs to open its vanishing electronic gap either by fabricating nanoribbons or by placing graphene on a suitable substrate. Magnetism can be induced in carbon nanostructures by interaction with magnetic molecules or nanoclusters or a magnetic substrate. Combining C nanostructures with a material with high SOC can be exploited to increase the SOC of the hybrid system. TMD have high SOC arising from the d orbitals of the transition metal atom. Monolayers of TMD can be direct gap semiconductors and have magnetic properties related to edges and/or unsaturated bonds. Finally, graphene/TMD heterostructures could inherit high-mobility from graphene and a finite gap and high SOC from TMD. I will address these issues using cutting-edge first principles computational techniques combining Density Functional Theory (DFT) and Non-Equilibrium Greens Function (NEGF) to compute electronic, magnetic and spin transport properties. For selected systems, I will also investigate spin transport for multiterminal devices in presence of external electric and/or magnetic field, in order to model realistic devices.

• DFG Programme: Research Grants