Since the discovery of the low-temperature, long-range ferromagnetic order in monolayers Cr₂Ge₂Te₆ and CrI₃, many efforts have been made to achieve a room temperature (RT) ferromagnet. The outstanding deformation ability of two-dimensional (2D) materials provides an exciting way to mediate their intrinsic ferromagnetism (FM) with strain engineering. Here, we summarize the recent progress of strain engineering of intrinsic FM in 2D van der Waals materials. First, we introduce how to explain the strain-mediated intrinsic FM on Cr-based and Fe-based 2D van der Waals materials through ab initio Density functional theory (DFT), and how to calculate magnetic anisotropy energy (MAE) and Curie temperature (T_C) from the interlayer exchange coupling J. Subsequently, we focus on numerous attempts to apply strain to 2D materials in experiments, including wrinkle-induced strain, flexible substrate bending or stretching, lattice mismatch, electrostatic force and field-cooling. Last, we emphasize that this field is still in early stages, and there are many challenges that need to be overcome. More importantly, strengthening the guideline of strain-mediated FM in 2D van der Waals materials will promote the development of spintronics and straintronics.

Since the experiments found that two-dimensional (2D) materials such as single-layer MoS₂ can withstand up to 20% strain, strain-modulated magnetism has gradually become an emerging research field. However, applying strain alone is difficult to modulate the magnetism of single-layer pristine MoS₂, but applying strain combined with other tuning techniques such as introducing defects makes it easier to produce and alter the magnetism in MoS₂. Here, we summarize the recent progress of strain-dependent magnetism in MoS₂. First, we review the progress in theoretical study. Then, we compare the experimental methods of applying strain and their effects on magnetism. Specifically, we emphasize the roles played by web buckles, which induce biaxial tensile strain conveniently. Despite some progress, the study of strain-dependent MoS₂ magnetism is still in its infancy, and a few potential directions for future research are discussed at the end. Overall, a broad and in-depth understanding of strain-tunable magnetism is very necessary, which will further drive the development of spintronics, straintronics, and flexible electronics.

The magnetic properties and clustering behaviors of the transition-metal (TM)-doped ZnO have been studied by first-principles calculations. We demonstrate the relationship between the types of TM (Co, Fe, Ni, and Cu) pairs and the energetic most stable configurations in ZnO:TM. Further calculations show that Co pairs have no tendency to form clusters, showing paramagnetic (PM) state in ZnO:Co samples in an equilibrium state and without excessive defects, as evidenced by various experiments, while ferromagnetic (FM) state is possible for the samples prepared under non-equilibrium conditions. Finally, systematical studies of a series of TM elements reveal different types of TM pairs in terms of clustering behaviors determined by spin-polarized and non-spin-polarized contributions: Co pairs and Fe pairs have no tendency to form clusters, showing PM and FM states, respectively, while Ni pairs and Cu pairs have a clustering tendency and show intrinsic FM ordering.

Undoped ZnO thin films are prepared by polymer‐assisted deposition (PAD) and treated by postannealing at different temperatures in oxygen or forming gases (95% Ar + 5% H₂). All the samples exhibit ferromagnetism at room temperature (RT). SQUID and positron annihilation measurements show that post‐annealing treatments greatly enhance the magnetizations in undoped ZnO samples, and there is a positive correlation between the magnetization and zinc vacancies in the ZnO thin films. XPS measurements indicate that annealing also induces oxygen vacancies that have no direct relationship with ferromagnetism. Further analysis of the results suggests that the ferromagnetism in undoped ZnO is induced by Zn vacancies.