# Recent Progress on Irradiation-Induced Defect Engineering of Two-Dimensional 2H-MoS2 Few Layers
## 6 Irradiation-Induced Properties
### Magnetic Properties  
2H-MoS\({}_{2}\) bulks are temperature-dependent diamagnetic [184]. It was reported that irradiation improved magnetic ordering in single crystals of MoS\({}_{2}\)[85]. [PERSON] et al. [77] investigated electron-irradiation-induced magnetic behaviors of MoS\({}_{2}\) crystals. The irradiation was carried out under 30 keV electrons with exposure time of 30 min. The effective magnetic moment of single crystals increased from 0.42 \(\upmu_{\text{B}}\) per Mo-ion to 1.11 \(\upmu_{\text{B}}\) per Mo-ion on account of irradiation. [PERSON] et al. [74] investigated magnetism of electron-irradiated MoS\({}_{2}\) single crystals. The diamagnetic MoS\({}_{2}\) single crystals transformed into ferromagnetic state after irradiation up to room temperature, as shown in Figure 34. The irradiation-induced magnetic phase transition was largely attributed to the strain around the irradiation-induced vacancies. Figure 33: (**a**) \(I_{D}\)-\(V_{DS}\) curves of the single-layer MoS\({}_{2}\) device after different plasma exposure time [128]. (**b**) Resistance of the device as a function of plasma exposure time [128]. Republished with permission of RSC Publisher, from Reference [128]. © 2014. Permission conveyed through Copyright Clearance Center, Inc.  
[PERSON] et al. [85] irradiated MoS\({}_{2}\) sheets with a thickness of 200 \(\upmu\)m at room temperature using a 3.5 MeV proton ion beam. The pristine sample was diamagnetic in nature. After irradiated at a fluence of \(1\times 10^{18}\) ions/cm\({}^{2}\), ferromagnetic ordering was induced in the MoS\({}_{2}\), as shown in Figure 35a. More detailed work indicated that the induced magnetization depended on the irradiation dose. Figure 35b shows the magnetization of irradiated MoS\({}_{2}\) crystalline flakes that were measured at 300 K and 5 kOe as a function of proton ion fluence from \(1\times 10^{17}\) ions/cm\({}^{2}\) to \(5\times 10^{18}\) ions/cm\({}^{2}\). The magnetization of the pristine flakes was negative as well as in irradiated flakes at a fluence of \(1\times 10^{17}\) ions/cm\({}^{2}\). The magnetization became positive after the sample was irradiated at a fluence of \(2\times 10^{18}\) ions/cm\({}^{2}\) and increased with the irradiation doses. However, the magnetization decreased when the flakes were irradiated at a fluence of \(5\times 10^{18}\) ions/cm\({}^{2}\). [PERSON] et al. [85] also exposed MoS\({}_{2}\) crystals (200 \(\upmu\)m thickness) under 0.5 MeV proton irradiation at an ion fluence of \(1\times 10^{18}\) ions/cm\({}^{2}\) (same fluence at which magnetic ordering was observed using 2 MeV protons) while ferromagnetism was not observed in the low-energy proton irradiation. After annealing at 350 \({}^{\circ}\)C for 1 h in Ar flow, a weak magnetic hysteresis loop was observed. The weak magnetic signal was also observed in the irradiated samples at a lower fluence of \(2\times 10^{17}\) ions/cm\({}^{2}\) and a lower energy of 0.5 MeV proton irradiation. Based on these phenomena, the appearance of observed magnetism in proton-irradiated MoS\({}_{2}\) flakes were due to a combination of defect moments arising from vacancies, interstitials, deformation and partial destruction of the lattice structure, such as the formation of edge states and reconstructions of the lattice. [PERSON] et al. [185] reported weak ferromagnetism phenomenon in MoS\({}_{2}\) nanosheets and attributed the magnetic properties to the presence of unsaturated edge atoms. Later, first-principles computations and density-functional theory calculations were carried out to predict ferromagnetism in zigzag nanoribbons of MoS\({}_{2}\)[186; 187; 188], magnetism in MoS\({}_{2}\) clusters [189], and magnetic edge state of hydrodesulfurizated MoS\({}_{2}\) particles [190]. It was generally accepted that [191] zigzag MoS\({}_{2}\) edges were ferromagnetic and metallic whereas armchair MoS\({}_{2}\) edges were nonmagnetic and semiconducting. The predication was experimentally approved in MoS\({}_{2}\) few-layers [192].