2024/10/17(Thu) 10:30 -12:00 五樓第一會議室 5F, 1st Meeting Room
Title
Unveiling a novel class of magnetism: the altermagnetism
Speaker
Dr. Danru Qu (Center for Condensed Matter Sciences)Abstract
The field of magnetism has seen a surge of interest in a novel classification known as altermagnetism over the past few years [1]. This interest is driven by the unique physical properties of altermagnetic materials, which takes advantages of both conventional antiferromagnets and ferromagnets through the altermagnetic spin-splitting effect (ASSE). The non-relativistic ASSE enables the generation of not only a longitudinal spin polarized current, but also a transverse pure spin current upon the injection of a charge current along certain crystal orientations. However, experimentally unequivocal observation of the ASSE is challenging. This difficulty arises from the inevitable mixing of ASSE with the spin Hall effect (SHE) caused by the material's relativistic spin-orbit coupling and the ASSE's dependence on the hard-to-probe and hard-to-control Néel vectors.
In this talk, I will discuss our approach in addressing these challenges in the study of ASSE in RuO2 [2]. Our experimental observations revealed a highly anisotropic spin-to-charge conversion in the epitaxial RuO2 thin film. We attribute the anisotropy to an altermagnetic origin by ruling out the complication of an anisotropic SHE. We found the IASSE exhibited an opposite sign compared to the inverse spin Hall effect (ISHE). Remarkably, the efficiency of the IASSE was found to be consistently 70% of that of the ISHE in RuO2 for thicknesses ranging from 5 nm to 32 nm. Furthermore, we demonstrated that the ASSE/IASSE effects are observable only when the Néel vectors are well-aligned by modifying the Néel vector domains via RuO2 crystallinity through different substrates. Interestingly, the shape of the thermal voltage hysteresis loop is anisotropic and is consistent with the anisotropic magnetic hysteresis loop of YIG, which verifies the [001] orientation of the RuO2 Néel vectors. Our study provides significant insights into the spin-splitting effect in altermagnetic materials, paving the way for future advancements in spintronic technologies.
[1] Libor Šmejkal, Jairo Sinova, and Tomas Jungwirth, Emerging Research Landscape of Altermagnetism. Phys. Rev. X 12, 040501 (2022).
[2] C.-T. Liao, Y.-C. Wang, Y.-C. Tien, S.-Y. Huang, and D. Qu, Separation of Inverse Altermagnetic Spin-Splitting Effect from Inverse Spin Hall Effect in RuO2. Phys. Rev. Lett. 133, 056701 (2024), Editors’ suggestion
Language
演講語言 (Language): in English
Hosted by