Tuning Magnetic Phases in Fe₃GaTe₂: Co Doping as a Gateway to Room-Temperature Ferromagnetism and Antiferromagnetism

Two-dimensional (2D) ferromagnetic materials such as CrI₃, Cr₂Ge₂Te₆, or some of the Fe-based van der Waals crystals have unique properties at the atomic level. They are unbelievably thin—just a few atoms thick—yet they exhibit tunable magnetism and excellent spin transport capabilities which make them perfect candidates for technologies like data storage, magnetic sensing and even quantum computing. But there’s one major challenge which is most of these 2D magnetic materials have low Curie temperatures—that’s the temperature where their ferromagnetism breaks down. Unfortunately, for many, this Curie point is way below room temperature. That’s a major issue when you’re trying to build devices that need to operate reliably in real-world environments. Fe₃GaTe₂, (FGaT) material has been getting a lot of attention because it’s one of the few 2D ferromagnets with a Curie temperature comfortably above room temperature—between 350 and 380 K, and the above-room-temperature Curie point can be further enhanced to 420 K by interface engineering and maintained in monolayer. It also stands out for its strong perpendicular magnetic anisotropy, high saturation magnetization, and excellent spin polarization. Basically, it’s got the right mix of features for next-generation devices like magnetic tunnel junctions (MTJs). That said, FGaT has its limitations. To really tap into its potential, researchers need ways to fine-tune its magnetic properties—things like magnetization strength, anisotropy, and phase behavior. One of the best ways to do this is through elemental doping. By swapping out certain atoms in the material’s structure, scientists can tweak how electrons interact, which in turn adjusts its magnetic and electronic behavior. While doping has worked wonders in other 2D materials, Co (cobalt) doping in Fe₃GaTe₂ remains underexplored. Related systems, like Fe₄GeTe₂, show that adding Co can trigger fascinating shifts between ferromagnetic and antiferromagnetic phases. But what happens in Fe₃GaTe₂? How do the concentration and placement of Co atoms impact its magnetic behavior? A research team (Jie Yu, Wen Jin, Gaojie Zhang, Hao Wu, Bichen Xiao, Li Yang ) from the School of Materials Science and Engineering at Huazhong University of Science and Technology, led by Professor Haixin Chang, recently set out to answer these questions. Their study, published in Physical Chemistry Chemical Physics, investigated how Co doping affects Fe₃GaTe₂ using advanced first-principles calculations.

The researchers began by building a crystal model that mimicked the hexagonal structure of pure Fe₃GaTe₂. This structure has two types of iron (Fe) sites, named Fe1 and Fe2. To figure out what happens when Co atoms are introduced, the team swapped out these Fe sites with Co atoms in different amounts. The goal was to see how the material would react both magnetically and energetically as it shifted between ferromagnetic (FM) and antiferromagnetic (AFM) phases. What they found was pretty interesting. Co atoms seemed to prefer taking over the Fe1 sites, especially when the concentration of Co was low. This preference matters because Fe1 atoms are the ones primarily responsible for the material’s magnetic strength. At low doping levels—when just two Co atoms replaced Fe sites (called 2Co-2)—the system remained ferromagnetic. However, small changes began to show up in the material’s magnetic behavior. Specifically, the Fe1 sites became slightly more ferromagnetic, with their magnetic moment increasing to around 2.08 µB. Meanwhile, Fe2, which is naturally less ferromagnetic, contributed even less than before. This finding suggested that adding a small amount of Co could boost magnetism in specific regions without disrupting the material’s overall ferromagnetic state. Things changed quite a bit when more Co atoms were added. In cases with four Co atoms replacing Fe sites (4Co-3), the total magnetic moment dropped significantly. This sharp decline hinted at a transition from ferromagnetism to antiferromagnetism. The shift happened because, as Co atoms increasingly took over Fe2 sites, the magnetic coupling between Fe and Co atoms weakened. The pristine Fe₃GaTe₂’s strong ferromagnetic interactions began to break down, allowing antiferromagnetic coupling to take over. This finding is particularly exciting because it shows that you can fine-tune magnetic phases—switching between FM and AFM states—just by adjusting how much Co gets added. That has serious potential for applications that need controlled magnetic switching. To get a clearer picture, the team dug deeper into the spin-polarized electronic band structures and densities of states for different doping levels. For the 2Co-2 case, they noticed a slight dip in spin polarization near the Fermi energy, caused by the presence of Co atoms introducing extra spin-down states. But in the 4Co-3 case, spin polarization partially recovered due to stronger interactions between the increased Co atoms and Fe atoms. When they looked at spin-polarized charge densities, it became even clearer that Fe1 sites played a leading role in magnetism. The maps also revealed symmetrical spin-up and spin-down charge distributions in AFM states, which confirmed antiferromagnetic coupling and the loss of net magnetization at higher Co levels. It’s a fascinating example of how small tweaks to doping can drastically change a material’s behavior.

In conclusion, the study led by Professor Haixin Chang and his team marks an important step forward for 2D magnetic materials, especially when it comes to spintronics and next-gen magnetic devices. By taking a close look at how Co doping affects Fe₃GaTe₂, the researchers shed light on new ways to fine-tune and control key magnetic properties like magnetization, spin polarization, and phase transitions. This is a big deal because Fe₃GaTe₂ is already one of the few 2D ferromagnets that works above room temperature. The ability to tweak its behavior even further through doping opens up a world of new possibilities. One of the most exciting takeaways from this study is the discovery that Co doping can trigger a shift from FM to AFM phases. This ability to switch magnetic states makes Fe₃GaTe₂ incredibly promising for applications like spin valves and magnetic memory devices, where such transitions are crucial. On top of that, the findings about spin polarization—how it changes with different doping levels—are especially useful for improving magnetoresistance in devices like MTJs. The researchers showed that spin polarization near the Fermi energy could be suppressed or restored, depending on the concentration of Co. This kind of control could lead to more efficient charge transport and better signal processing in nanoscale spin-based devices. From a practical standpoint, this work has some exciting real-world applications. Materials that can switch between FM and AFM states could help create more compact, energy-efficient memory storage devices. Beyond that, these findings are relevant for quantum technologies, where precise control of magnetism and spin polarization at the atomic scale plays a major role in improving performance.