Control of magnetic transitions via interlayer engineering in ferroelectric HO-OH systems.

Controlling magnetic phase transitions in two-dimensional (2D) multiferroics is crucial for both fundamental scientific knowledge and practical applications. Here, we present a general strategy for inducing magnetic transitions in 2D ferroelectrics based on the electron pairing principle. First-principles calculations revealed the coupled ferroelectric and ferromagnetic behavior in water-hydroxyl (HO-OH) monolayer, with ferromagnetism arising from unpaired electrons in 2p bonding orbitals of the OH groups. A ferromagnetic-to-nonmagnetic phase transition occurs via interlayer coupling, forming HO molecules where electrons pair up. Conversely, the nonmagnetic-to-ferromagnetic transition can be triggered by stacking rearrangements that prevent HO formation and restore unpaired electrons. Importantly, such magnetic transitions can be efficiently controlled by external electric fields. Notably, low-energy-electron-assisted synthesis method and high-resolution scanning tunneling microscopy confirm the successful creation of HO-OH overlayer on Ag(111). These findings provide an approach for magnetism control in 2D ferroelectrics and offer insights for future spintronic and multiferroic devices.