Unexpected Photoinduced Room Temperature Magnetization in Bi2WO6 Nanosheets

Abstract The current investigation in magnetism in 2D materials offers new opportunities for studying spintronics at low dimensions. Here, reversible photoinduced room temperature magnetization in 2D Bi 2 WO 6 nanosheets is reported for the first time. Compared with the original state, the ultraviolet (UV)‐illuminated Bi 2 WO 6 nanosheets show a yellow‐green color change and significantly enhanced magnetic signals (saturated magnetization ( M s ) increased from 0.002 to 0.12 emu g −1 ). X‐ray photoelectron spectroscopy (XPS) results show unexpected W reduction (W 6+ to W 5+ /W4+) and Bi oxidation (Bi 3+ to Bi 5+ ) upon UV illumination for the Bi 2 WO 6 nanosheets, indicating a photoexcited Bi to W charge transfer. Density functional theory (DFT) calculations indicate spontaneous spin polarization of the Bi 2 WO 6 nanosheets in the excited metastable state. Meanwhile, thicker Bi 2 WO 6 nanoplates or nanoparticles show no enhanced magnetic signals upon UV illumination. UV illumination of the thin Bi 2 WO 6 nanosheets can induce the formation of internal electric field (polarization), leading to structural deformation/lattice distortion (photostriction). The photoexcited electrons are trapped in the WO 6 layers while the photogenerated holes are trapped in the Bi 2 O 2 layers, leading to spin polarization and enhance the magnetization. The research may bring some new insights in tuning the magnetic properties of 2D nanostructures.