Robust room temperature ferromagnetism in an itinerant van der Waals antiferromagnet

Abstract: The coexistence of antiferromagnetic and ferromagnetic order at room temperature in single-phase van der Waals materials, particularly within the two-dimensional limit, has attracted significant research interest. Nonetheless, such materials are rare. In this work, we introduce an itinerant van der Waals antiferromagnet (Fe0.56Co0.44)5GeTe2, where the ferromagnetic order of its exfoliated flakes remains discernible up to room temperature, extending down to the monolayer limit. A notable phenomenon observed is the evident odd-even layer-number effect at high temperature (e.g., T = 150 K). Such behaviour can be expounded by a linear-chain model. Of particular interest is the robust ferromagnetic order observed in even-layer flakes at low temperature (e.g., T = 2 K), which could potentially be attributed to spin-polarized defects. The intricate interplay among magnetic field strength, layer number, and temperature gives rise to a diverse array of phenomena, holding promise not only for new physics but also for practical applications.