YRLG Workshop: Correlation and Topology in magnetic materials, July 16th - 18th 2024
Adolfo O. Fumega
Layered van der Waals materials are one of the most promising platforms for engineering emergent phenomena in condensed matter physics. The weak van der Waals bonding between their layers allows to easily reach the single-layer limit, offering intrinsic degrees of freedom to artificially design new materials. For instance, monolayers of different compounds can be stacked together, and even a specific twist angle between stacked layers can be fixed, creating a moiré pattern that leads to novel heterostructures with emergent properties. Therefore, studying and discovering new van der Waals materials displaying different orders such as ferromagnetism, ferroelectricity or superconductivity in the monolayer limit has become a crucial task to develop new technologies using this bottom-up approach. Recently, the first purely two-dimensional multiferroic material was isolated, NiI2, establishing a new captivating building block to create van der Waals heterostructures.
Multiferroics are materials that display simultaneously more than one ferroic order. In particular, electric and magnetic orders can coexist in multiferroics and show a strong magnetoelectric coupling. This coupling between the orders makes multiferroics highly appealing from a technological point of view, as they could be used to control magnetic orders using electric fields. The recent discovery of multiferroicity in monolayer NiI2 has bridged the fields of multiferroics and van der Waals materials, paving the way to engineer multiferroic-based van der Waals heterostructures with emergent functionalities.
In this presentation, we will demonstrate that the microscopic mechanism responsible for the emergence of a multiferroic order in monolayer NiI2 stems from the combination of a spin-spiral magnetic order and the strong spin-orbit coupling from iodine atoms [1]. We will show that this mechanism entails a strong magnetoelectric coupling, that can be exploited to prove and characterize the multiferroic order of monolayer NiI2 using a Scanning Tunneling Microscope (STM) [2]. Finally, we will show that the multiferroic domains can be controlled with external electric fields using the tip of the STM.
[1] Adolfo O Fumega* and Jose L Lado,* “Microscopic origin of multiferroic order in monolayer NiI2,” 2D Materials 9, 025010 (2022) [2] Mohammad Amini,* Adolfo O. Fumega,* Héctor González-Herrero, Viliam Vaňo, Shawulienu Kezilebieke, Jose L. Lado,* and Peter Liljeroth,* “Atomic-scale visualization of multiferroicity in monolayer NiI2,” Advanced Materials, 2311342 (2024)