- 30 Jan 2023
Louis Veyrat I Magnetotransport in antiferromagnetic thin films
Antiferromagnets, and in particular collinear antiferrmoagnets, have been gathering a lot of interest recently in a range of different topics, from the field of topology with the magnetic topological insulators, to the interest for spintronic in antiferromagnets and the newly predicted altermagnets. In general, the antiferromagnetic state and spin texture can strongly modify the magnetotransport properties and lead to novel effects.
In this seminar, I will present our recent work on how magnetic and in particular antiferromagnetic texture can affect magnetotransport phenomena in epitaxial thin film. I will focus on two systems, LaTiO3/SrTiO3 (LTO/STO) and RuO2. In thin LTO films (3u.c. to 10u.c.), concentrating on the longitudinal magnetoresistance, we observed at low temperature a linear magnetoresistance (LMR) with colossal amplitude above 6000% at 9T. The LMR is compatible with the existence of low-mobility regions, which contrasts with the very high mobility observed in the films (up to 40 000cm2/V.s). Through cryogenic Lorentz transmission electron microscopy, we identify the presence of a magnetic stripe pattern in the LTO layer compatible with spiral magnetism, which has similar coverage and temperature dependence as the low-mobility regions identified in magnetotransport. The magnetic origin of the lower mobility regions induces an unusual combination of very high coverage and very high mobility, resulting in a colossal LMR amplitude.
In the altermagnet RuO2, we focused on the Hall effect, where a novel type of anomalous Hall effect (AHE) was recently predicted[1,4], despite the collinear antiferromagnetic state, due to additional symmetry lowering caused by the non-magnetic oxygen octahedrons. This is an example of the so-called altermagnetism, which is characterised by different symmetries as compared to usual colinear antiferromagnets. In thin films hallbars, we indeed observed an AHE, which is not associated with any net magnetisation, confirming recent other observation. Additionally, we observed the saturation of the AHE at very high magnetic field. This is a very promising result which we expect will further the growing interest in altermagnetic materials.
 M. M. Otrokov et al., “Prediction and observation of an antiferromagnetic topological insulator,” Nature, vol. 576, no. 7787, pp. 416–422 (2019)
 L. Šmejkal, J. Sinova, and T. Jungwirth, “Beyond Conventional Ferromagnetism and Antiferromagnetism: A Phase with Nonrelativistic Spin and Crystal Rotation Symmetry,” Phys. Rev. X, vol. 12, no. 3, p. 031042, (2022)
 T. Tschirner et al., “Linear colossal magnetoresistance driven by magnetic textures in LaTiO3 thin films on SrTiO3,” vol arXiv 2210.07682 (2022)
 L. Šmejkal, R. González-Hernández, T. Jungwirth, and J. Sinova, “Crystal time-reversal symmetry breaking and spontaneous Hall effect in collinear antiferromagnets,” Sci. Adv., vol. 6, no. 23, p. eaaz8809, (2020)
 Z. Feng et al., “Observation of the Anomalous Hall Effect in a Collinear Antiferromagnet,” arXiv 2002.08712 (2020)
 T. Tschirner et al., in preparation “