Realizing soft two-dimensional room-temperature magnets in oxidized (Fe₇₅Co₂₅)₅GeTe₂

Two-dimensional (2D) van der Waals (vdW) magnets have demonstrated intriguing functionalities in spintronic devices and have drawn enormous interest. Nevertheless, the development of soft in-plane 2D magnets with low coercivity remains limited. In this study, we fabricated a high-quality (Fe₇₅Co₂₅)₅GeTe₂ crystal and achieved a soft in-plane 2D magnet with coercivity of approximately 3 Oe in a naturally oxidized (Fe₇₅Co₂₅)₅GeTe₂ flake at room temperature. A combination of X-ray magnetic circular dichroism (XMCD) and ferromagnetic resonance (FMR) revealed a high Curie temperature of ~350 K and relatively low magnetic damping at room temperature. Kerr microscopy further demonstrated that the oxidized flakes exhibited exchange bias and an unconventional reduction in coercivity compared with their non-oxidized counterparts at liquid nitrogen temperatures. Detailed analyses using transmission electron microscopy (TEM) and density functional theory (DFT) calculations attribute this behavior to modifications in magnetic anisotropy and interlayer exchange coupling induced by oxygen intercalation. These findings deepen the understanding of the magnetic properties of the cobalt-doped Fe₅GeTe₂ family and highlight the potential of oxidation modulation in 2D vdW magnets, positioning (Fe₇₅Co₂₅)₅GeTe₂ as a promising candidate for next-generation spintronic devices.