Robust Weak Antilocalization Effect Up to similar to 120 K in the van der Waals Crystal Fe5-x GeTe2 with Near-Room-Temperature Ferromagnetism

The van der Waals Fe5-x GeTe2 is a 3d ferromagnetic metal with a high Curie temperatureof 275 K. We report herein the observation of an exceptional weakantilocalization (WAL) effect that can persist up to 120 K in an Fe5-x GeTe2 nanoflake, indicatingthe dual nature with both itinerant and localized magnetism of 3delectrons. The WAL behavior is characterized by the magnetoconductancepeak around zero magnetic field and is supported by the calculatedlocalized nondispersive flat band around the Fermi level. The peakto dip crossover starting around 60 K in magnetoconductance is visible,which could be ascribed to temperature-induced changes in Fe magneticmoments and the coupled electronic band structure as revealed by angle-resolvedphotoemission spectroscopy and first-principles calculations. Ourfindings would be instructive for understanding the magnetic exchangesin transition metal magnets as well as for the design of next-generationroom-temperature spintronic devices.