Antiferromagnetic spin transport - from Hematite to Orthoferrites

• Applicants: Professor Dr. Mathias Kläui; Professor Dr. Ulrich Nowak
• Subject Area: Experimental Condensed Matter Physics ; Theoretical Condensed Matter Physics
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 423441604

Spintronics is a field of research that focuses on the transport and control of angular momentum in typically nano-structured materials. For the transport of angular momentum, traditionally spin-polarized electrons have been used as the carrier in metals. More recently, the focus has shifted to using magnonic spin currents, which can exist in low damping magnetic insulators without ohmic losses. For this burgeoning field of insulator spintronics conventionally ferrimagnetic insulators have been developed and only recently antiferromagnets were demonstrated to exhibit favourable properties as active components, since essential functionalities of antiferromagnets - electrical reading and writing - have been demonstrated. Antiferromagnetic insulators, specifically, have recently gained attention due to their low loss spin transport and ultra-fast dynamics boding well for use in next-generation spintronic devices. Hematite, the main constituent of rust, is a type of insulating antiferromagnetic mineral, which is a promising candidate in this context due to its ability to transport spin information over long distances, which has been in the focus of our preceding joint project. Within this follow-up proposal, we want to exploit the ability of Hematite to be doped to flexibly tune its magnetic and transport properties and study in particular the impact of the anisotropy on the spin transport. Beyond hematite, we extend our study to a promising class of dielectric antiferromagnets, which is rare-earth orthoferrites. While related to Hematite in terms of their magnetic properties, these materials can exhibit a wide range of strongly anisotropic properties leading to spin reorientation transitions, weak ferromagnetism, as well as tunable damping. This project will synergetically combine experimental and theoretical approaches to investigate and understand the mechanisms of magnonic spin transport in selectively doped hematite and particular orthoferrites. The necessary sample growth of thin hematite and orthoferrite films will be developed and optimized, while at the same time parameterizing spin models on the basis of ab initio calculations. The magnetostatic and dynamic properties are then investigated by a combination of magneto-transport measurements, magnetic imaging and multiscale simulations. The main goal is the understanding of the effects of the composition and doping on the magnetic transport. Furthermore, the project will probe the transport of angular momentum by hybrid quasiparticles, such as magnon-phonon polarons. Having understood the transport properties, we will finally explore the potential of these materials for use in novel device concepts by controlling lateral transport using local gating and vertical transport across a magnon spin valve. In conclusion, this project will underpin very promising current research efforts to exploit the advantages of antiferromagnetic insulators for the development of new spintronic devices.

• DFG Programme: Research Grants