Ferromagnetism of single atoms above room temperature

The demands of the information era, driven by cloud computing and big data, necessitate high-density storage systems. In magnetic recording media, reducing bit size is crucial for significantly increasing areal density. Consequently, using single atoms as recording bits offers the potential to achieve unprecedented areal densities. However, achieving ferromagnetism in single atoms typically requires very low temperatures, and synthesizing large areas of single atoms for recording media remains a significant challenge. In this study, a straightforward mixing and stirring method was employed to intercalate a large number of Ni single-atoms into MoS₂ nanosheets. Remarkably, room-temperature ferromagnetism was observed in all samples. Specifically, the 2% Ni-doped MoS₂ exhibited a magnetic moment of 0.53 µ_B, which is close to the theoretical value. The magnetization depends on the bonding between nickel and sulfur atoms. In 2% Ni-doped MoS₂, nickel prefers to form Ni-S bonds, while at higher doping concentrations, S-Ni-S bonding is more prevalent, leading to antiferromagnetic coupling. The observed ferromagnetism in these higher-concentration-doped samples may be attributed to strain in the nanosheets induced by nickel intercalation or nanostructured NiS particles.