Magneto-Thermo-Electric Effects In Antiferromagnetic Spintronics – MATHEEIAS

This project will identify and exploit novel transport mechanisms in complex antiferromagnets (AFs). We will focus on crystalline, topological, and anomalous origins of the spin Hall effect, spontaneous Hall effect (HE) and their thermal counterparts (Nernst effects), arising in part by the spontaneous symmetry breaking in AFs. The project addresses fundamental questions in an emerging branch of spintronics based on transport phenomena governed by crystal symmetry, topology, and its interplay with AF order. This combination could prove essential for the development of robust large effects vital in new device concepts in the very active field of AF spintronics.
In the field of spintronics, the inter-conversion between charge and spin currents has facilitated the progress of fundamental physics and fostered the emergence of new applications. In the past decade, it has emerged that the chief mechanism responsible for spin-charge conversion, the spin HE (SHE), reveals itself under various flavors. Indeed, HEs are either associated to the spin deflection upon extrinsic or intrinsic spin-orbit coupling (“anomalous” HE, AHE), to the non-trivial spin structures (“topological” HE, THE), or to specific atomic arrangements that break time- and spatial-reversal symmetry combinations (“crystal” HE, CHE). AFs are excellent platforms to investigate these different mechanisms, and their thermal (Nernst) counterparts, arising from the interplay of their band and spin structures.
Note that the CHE has not yet been observed in experiment, and that crystal Nernst physics has not been addressed at all. Therefore, these effects are a key focus of our proposal. Another key feature of the project lies in the choice of the material (Mn5Si3) that will serve as a versatile platform to investigate the above mechanisms. The metamagnetic phase transition of Mn5Si3 (AF with a chiral spin structure below 65K and collinear above) will be used, e. g., to demonstrate and control the relative contributions of CHE and THE, and their thermal counterparts, respectively. This approach, based on the systematic study of a model system, is key to disentangle the origins of the Hall and Nernst responses. The proposed research program thus responds to the need for new knowledge and experimental designs that are essential to better understand, disentangle, and take advantage of these effects.
The key aims of this program are to:
- grow high-quality ordered Mn5Si3 thin films;
- experimentally observe and theoretically model the CHE, THE and other Hall as well as Nernst effects in Mn5Si3 with different non-trivial spin structures, crystal orientations, and elastic strain;
- test the assumed validity and universality of the Mott relation between charge and thermal transport in AFs with non-trivial topology;
- investigate the impact on the inverse SHE by non-linear spin fluctuations near magnetic phase transitions, and exploit this effect to probe the magnetic order parameter variations.