Modeling interface disorder effects on the spin transport through an antiferromagnetic insulator

• Applicant: Dr. Niklas Rohling
• Subject Area: Theoretical Condensed Matter Physics
• Term: from 2018 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 417034116

Antiferromagnetic insulators (AFIs) have several properties which are beneficial for spintronics: the absence of Joule heating from the spin transport, the faster dynamics compared to ferromagnetic insulators (FIs), and the absence of a coupling to magnetic fields. Recent experiments show that a thin AFI layer can enhance the spin transport from the FI yttrium iron garnet (YIG) into a metal like platinum. However, the coupling mechanism at the interfaces has so far not been analyzed in detail in theory. The interaction between the two sides of the respective interface was described by one effective parameter in the models. The experiments, on the other hand, show a variance from sample to sample. The strongest spin transport was achieved with polycrystalline AFI layers while monocrystalline layers did not lead to an enhancement of the spin signal. These experimental findings indicate that the specific properties of the AFI layer - and for a very thin layer this means especially the properties of the interfaces -determine the spin transport. These interfacial properties cannot be comprised by a single parameter for the interfacial coupling.The central question of the research project proposed here is whether disorder at the interface hampers or supports spin transport.Concretely, we will investigate(i) the anisotropy of the spin transport in AFIs, especially in NiO,(ii) a model which represents the roughness of the interface by a random contribution to the exchange interaction across the interface, and(iii) scattering at crystallographic defects.In order to compute the spin current through the interfaces, and this beyond the first order in the interfacial interaction, we will extend the formalism of Green's functions to magnonic transport in AFIs. The adaptation of methods which have been developed for electric transport through rough interfaces will allow for taking into account the disorder at the AFI interfaces.A successful work on this project will result in significant insights into the coupling at the interface of an AFI. This will yield recommendations for the preparation of the respective interfaces in experiments, as the influence of the roughness of the interface will be known. Moreover, a theoretical method will be available which allows for further computations of the spintransport in AFIs or in multilayers, e.g. those calculations which aim at quantum effects within the magonic spin transport.

• DFG Programme: Research Grants