• High-pressure experiments on NiI2 flakes demonstrate a reversible transition from a helimagnetic to an antiferromagnetic state at approximately 7 GPa.
• The transition is accompanied by an increase in magnetic transition temperatures for both helimagnetic and antiferromagnetic states at lower pressures.
• Monte Carlo simulations suggest that the second-nearest neighbor interlayer interaction plays a significant role in facilitating the observed magnetic phase transition.

A comprehensive study investigated the magnetic properties of NiI2 flakes, a van der Waals (vdW) magnet, under hydrostatic pressures up to 11 GPa. The research revealed a reversible transition from a helimagnetic (HM) to an antiferromagnetic (AFM) state at approximately 7 GPa. Prior to this transition, the material exhibits an increase in magnetic transition temperatures for both magnetic states under low pressures. Experimental techniques including Raman spectroscopy and second harmonic generation (SHG) were used, complemented by Monte Carlo simulations, to understand the role of interlayer interactions in driving this transition. This research enhances understanding of 2D magnetic materials.

• What: NiI2 flakes undergo a pressure-induced magnetic phase transition from a helimagnetic to an antiferromagnetic state.
• Who: Researchers from Shenzhen Technology University, Southern University of Science and Technology, Tsinghua University, Max Planck Institute, The University of Hong Kong, and Yangzhou University
• When: Experiments conducted up to 11 GPa pressure, with a key transition observed at approximately 7 GPa. Published May 7, 2025.
• Where: Experiments performed in a laboratory setting using a diamond-anvil cell (DAC).

The study provides strong evidence for pressure-induced manipulation of magnetic order in NiI2, showcasing a transition from a helimagnetic to an antiferromagnetic state. The combination of experimental results (Raman spectroscopy and SHG) with Monte Carlo simulations strengthens the conclusions. The emphasis on interlayer interactions as a key factor in driving this transition offers valuable insights for designing and tuning magnetic properties in 2D materials. The pressure-induced enhancement of the magnetic transition temperature, along with the reversible nature of the helimagnetic-antiferromagnetic transition, could have implications for developing novel magnetic devices.

The research demonstrates that applying pressure to NiI2 flakes induces a magnetic phase transition from a helimagnetic to an antiferromagnetic state, with a critical point around 7 GPa. The transition is driven by the strengthening of interlayer interactions, as confirmed by both experimental and simulation results. These findings offer a pathway for controlling magnetic properties in 2D materials and could lead to advancements in nanoscale magnetic device technology. Further research could explore the detailed magnetic structure through neutron scattering under pressure.