Study Reveals Opposite Pressure Effects on Magnetic Phase Transitions in NiBr2 and NiI2

NiI₂ and NiBr₂ are van der Waals triangular-lattice multiferroics that host incommensurate helimagnetic order at the lowest temperatures. These materials are studied for their magnetic properties under varying conditions. The research examines the effects of hydrostatic pressure on their phase transitions.

In NiBr₂, increasing pressure suppresses the helimagnetic order and promotes a transition to a higher-symmetry magnetic phase. This behavior contrasts with NiI₂, where pressure stabilizes the helimagnetic state. The study used neutron scattering and other techniques to observe these changes.

The materials' triangular lattice structure contributes to their complex magnetic interactions. Frustration in the lattice leads to the incommensurate order observed below certain temperatures. Understanding pressure effects provides insights into tuning these properties.

pressure was applied up to several gigapascals in the experiments.

For NiBr₂, the helimagnetic propagation vector decreased with pressure, indicating a shift toward commensurate order. In NiI₂, the vector remained stable or increased slightly under similar conditions. These opposite responses highlight differences in electron correlations and spin-orbit coupling between the two compounds.

NiI₂ has stronger spin-orbit effects due to iodine's higher atomic number compared to bromine in NiBr₂. The findings were reported by a team using facilities at major neutron sources.

The research underscores how subtle chemical variations can lead to divergent pressure responses in similar materials.

This knowledge aids in designing multiferroics for applications in spintronics and sensors. Future studies may explore intermediate pressures or doping to further manipulate these phases. The work was published in Nature on a date corresponding to recent experimental data collection.