Xie, TiMagnetism has played a crucial role in both fundamental research and technological advancement, from ancient compasses to modern spintronics. With the advent of artificial intelligence and the increasing demand for high-volume data storage, there have been significant efforts to reduce the dimensionality of memory materials. Recently, the discovery of two-dimensional magnetic van der Waals materials has enabled the observation of long-range magnetic order in monolayer crystals, which exhibit high sensitivity to external stimuli such as optical incidence, mechanical strain, and chemical functionalization. Our systematic work focuses on the efficient control of two-dimensional magnetism through multiple external stimuli, including chemical, optical, electrical, and mechanical means. These works achieved the effective control of a wide range of magnetic properties of two-dimensional magnets, such as Curie temperatures, magnetic coercivities, domain profiles, and magnetic phases. These research achievements will provide valuable insights into the fundamentals of two-dimensional magnetism and its interplay with external stimuli, paving the way for advancing the nanoscale spintronic and photonic devices in ultrathin platforms.enDissertationCondensed matter physics