Origin of near-room-temperature itinerant antiferromagnetism in van der Waals magnet (Fe_0.65Co_0.35)₄GeTe₂

Metallic van der Waals (vdW) antiferromagnets with high Néel temperatures (T_N) serve as ideal platforms for spintronics applications. They offer distinct advantages over ferromagnets due to their negligible stray field, high‒frequency spin resonances, robustness against magnetic perturbation, and ultrafast spin dynamics. However, such materials are rare because achieving the antiferromagnetic (AFM) state, along with metallicity, requires a delicate balance between itinerant electronic conduction and magnetic exchange interactions. Here, we show how the vdW material (Fe_0.65Co_0.35)₄GeTe₂ overcomes these limitations, and hosts a near–room–temperature itinerant AFM state. The enhanced T_N in this system likely originates from the site-selective occupation of Fe and Co atoms, which minimizes structural randomness and magnetic frustration. Our study reveals a rich sequence of magnetic phases in (Fe_0.65Co_0.35)₄GeTe₂ across a broad temperature–magnetic field (T–H) phase space. Magnetoresistance (MR), Hall effect, and angular-dependent MR measurements exhibit clear signatures of multiple magnetic transitions, including temperature-driven spin reorientation and field-induced AFM–to–spin-flop (SF) and SF–to–ferromagnetic transitions. These features indicate strong coupling between localized moments and itinerant electrons, which mediates the magnetic interactions responsible for stabilizing the high–T_N AFM state. The experimental findings are further supported and elucidated by electronic structure and phase stability calculations. The discovery of a high–T_N state in (Fe_0.65Co_0.35)₄GeTe₂ vdW metal holds great potential for AFM spintronic devices.