Transition metal dichalcogenides (TMDs) enable magnetic property engineering via intercalation, but stoichiometry-structure-magnetism correlations remain poorly defined for Fe-intercalated NbSe2. Here, we report a systematic study of FexNbSe2 across an extended composition range 0.05≤x≤0.38, synthesized via chemical vapor transport and verified by rigorous energy-dispersive x-ray spectroscopy (EDS) microanalysis. X-ray diffraction, magnetic, and transport measurements reveal an intrinsic correlation between Fe content, structural ordering, and magnetic ground states. With increasing x, the system undergoes a successive transition from paramagnetism to a spin-glass state, then to long-range antiferromagnetism (AFM), and ultimately to a reentrant spin-glass phase, with the transition temperatures exhibiting a nonmonotonic dependence on Fe content. The maximum N\'eel temperature (TN = 175K) and strongest AFM coupling occur at x=0.25, where Fe atoms form a well-ordered 2a0×2a0 superlattice within van der Waals gaps. Beyond x=0.25, the superlattice transforms or disorders, weakening Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions and significantly reducing TN. Electrical transport exhibits distinct anomalies at magnetic transition temperatures, corroborating the magnetic state evolution. Our work extends the compositional boundary of Fe-intercalated NbSe2, establishes precise stoichiometry-structure-magnetism correlations, and identifies structural ordering as a key tuning parameter for AFM. These findings provide a quantitative framework for engineering altermagnetic or switchable antiferromagnetic states in van der Waals materials.
@article{arxiv.2512.18993,
title = {Stoichiometry-Controlled Structural Order and Tunable Antiferromagnetism in $\mathrm{Fe}_{x}\mathrm{NbSe_2}$ ($0.05 \le x \le 0.38$)},
author = {Xiaotong Xu and Bei Jiang and Runze Wang and Zhibin Qiu and Shu Guo and Baiqing Lv and Ruidan Zhong},
journal= {arXiv preprint arXiv:2512.18993},
year = {2026}
}