Monolayer Fe$_{3}$GaX$_{2}$ (X=I, Br, Sb): high-temperature two-dimensional magnets and a novel partially ordered spin state

We systematically investigated the effects of charge doping and strain on monolayer Fe$_3$GaTe$_2$, and proposed three new novel two-dimensional magnetic materials: monolayer Fe$_3$GaX$_2$ (X=I, Br, Sb). We found that both strain and charge doping can tune the magnetic interactions, and the tuning by charge doping is more significant. Differential charge analysis revealed that the doped charges predominantly accumulate around Te atoms. Based on this insight, we introduced Fe$_{3}$GaI$_{2}$, Fe$_{3}$GaBr$_{2}$, and Fe$_{3}$GaSb$_{2}$ monolayers. The Fe$_{3}$GaI$_{2}$ and Fe$_{3}$GaBr$_{2}$ monolayers contain I and Br atoms rather than Te atoms, emulate electron-doped Fe$_{3}$GaTe$_{2}$ monolayer, resulting in notably high T$_c$ values of 867 K and 844 K, respectively. In contrast, the Fe$_3$GaSb$_2$ monolayer mimics hole-doped Fe$_{3}$GaTe$_{2}$ monolayer, presents a mix of FM and antiferromagnetic interactions, manifesting a distinctive partially ordered magnetic state. Our study demonstrates that substitution atoms based on the charge-doping effect offer a promising approach for predicting new magnetic materials. The proposed Fe$_{3}$GaI$_{2}$, Fe$_{3}$GaBr$_{2}$, and Fe$_{3}$GaSb$_{2}$ monolayers hold great potential for spintronics applications, and may stimulate the pursuit of new types of spin liquid.