Giant 2D Skyrmion Topological Hall Effect with Ultrawide Temperature Window and Low-Current Manipulation in 2D Room-Temperature Ferromagnetic Crystals

The discovery and manipulation of topological Hall effect(THE),an abnormal magnetoelectric response mostly related to the Dzyaloshinskii–Moriya interaction(DMI),are promising for next-generation spintronic devices based on topological spin textures such as magnetic skyrmions.However,most skyrmions and THE are stabilized in a narrow temperature window either below or over room temperature with high critical current manipulation.It is still elusive and challenging to achieve large THE with both wide temperature window till room temperature and low critical current manipulation.Here,using controllable,naturally oxidized sub-20 and sub-10 nm 2D van der Waals room-temperature ferromagnetic Fe_(3)GaTe_(2-x)crystals,we report robust 2D skyrmion THE with ultrawide temperature window ranging in three orders of magnitude from 2 to 300 K,in combination with giant THE of~5.4μΩ·cm at 10 K and~0.15μΩ·cm at 300 K,which is 1–3 orders of magnitude larger than that of all known room-temperature 2D skyrmion systems.Moreover,room-temperature current-controlled THE is also realized with a low critical current density of~6.2×10^(5)A·cm^(-2).First-principles calculations unveil natural oxidation-induced highly enhanced 2D interfacial DMI reasonable for robust giant THE.This work paves the way to room-temperature electrically controlled 2D THE-based practical spintronic devices.

Enhanced Magnetic Interaction between Ga and Fe in Two-Dimensional van der Waals Ferromagnetic Crystal Fe_(3)GaTe_(2)

Fe_(3)GaTe_(2),a recently discovered van der Waals ferromagnetic crystal with the highest Curie temperature and strong perpendicular magnetic anisotropy among two-dimensional(2D)magnetic materials,has attracted significant attention and makes it a promising candidate for next-generation spintronic applications.Compared with Fe_(3)GeTe_(2),which has the similar crystal structure,the mechanism of the enhanced ferromagnetic properties in Fe_(3)GaTe_(2)is still unclear and needs to be investigated.Here,by using x-ray magnetic circular dichroism measurements,we find that both Ga and Te atoms contribute to the total magnetic moment of the system with antiferromagnetic coupling to Fe atoms.Our first-principles calculations reveal that Fe_(3)GaTe_(2)has van Hove singularities at the Fermi level in nonmagnetic state,resulting in the magnetic instability of the system and susceptibility to magnetic phase transitions.In addition,the calculation results about the density of states in ferromagnetic states of two materials suggest that the exchange interaction between Fe atoms is strengthened by replacing Ge atoms with Ga atoms.These findings indicate the increase of both the itinerate and local moments in Fe_(3)GaTe_(2)in view of Stoner and exchange interaction models,which results in the enhancement of the overall magnetism and a higher Curie temperature.Our work provides insight into the underlying mechanism of Fe_(3)GaTe_(2)’s remarkable magnetic properties and has important implications for searching 2D materials with expected magnetic properties in the future.