Circularly polarized light carries light spin angular momentum, which may lead helicity-resolved Raman scattering to be sensitive to the electronic spin configuration in magnetic materials. Here, we demonstrate that all Raman modes in the 2D ferromagnet VI3 show different scattering intensities to left and right circularly polarized light at low temperatures, which gives direct evidence of the time-reversal symmetry breaking. By measuring the circular polarization of the dominant Raman mode with respect to the temperature and magnetic field, the ferromagnetic (FM) phase transition and hysteresis behavior can be clearly resolved. Besides the lattice excitations, quasielastic scattering is detected in the paramagnetic phase, and it gradually evolves into the acoustic magnon mode at 18.5 cm–1 in the FM state, which gives the spin wave gap that results from large magnetic anisotropy. Our findings demonstrate that helicity-resolved Raman spectroscopy is an effective tool to directly probe the ferromagnetism in 2D magnets.

Like their biogenic counterparts, synthetic minerals with hierarchical architectures should exhibit multiple structural functions, which nicely bridge the boundaries between engineering and functional materials. Nevertheless, design of bioinspired mineralization approaches to thin coatings with distinct micro/nanotextures remains challenging in the realm of materials chemistry. Herein, a general morphosynthetic method based on seeded mineralization was extended to achieve prismatic-type thin CaCO coatings on fibrous substrates for oil/water separation applications. Distinct micro/nanotextures of the overlayers could be obtained in mineralization processes in the presence of different soluble (bio)macromolecules. These hierarchical thin coatings therefore exhibit multiple structural functions including underwater superoleophobicity, ultralow adhesion force of oil in water, and comparable stiffness/strength to the prismatic-type biominerals found in mollusk shells. Moreover, this controllable approach could proceed on fibrous substrates to obtain robust thin coatings, so that a modified nylon mesh could be employed for oil/water separation driven by gravity. Our bioinspired approach based on seeded mineralization opens the door for the deposition of hierarchical mineralized thin coatings exhibiting multiple structural functions on planar and fibrous substrates. This bottom-up strategy could be readily extended for the syntheses of advanced thin coatings with a broad spectrum of engineering and functional constituents.

We present a detailed study on the structural phase transition in α-TiBr3, which is deeply connected with the lattice and orbital degree of freedoms. A chemical vapor transport method is adopted to synthesize the α-TiBr3 single crystal samples, and the structural phase transition at about 180 K is characterized by x-ray diffraction (XRD), magnetic susceptibility, and specific heat capacity. To further the understanding in the physical nature of this phase transition, a systematic Raman spectroscopic study is performed on α-TiBr3 crystals. With temperature decreasing, a large frequency blue shift and peak width narrowing are observed in the vibrational mode associated with Ti in-plane relative movement, which indicates the formation of Ti–Ti bonding and orbital-fluctuation freezing at low temperatures. These results are fully consistent with magnetic–nonmagnetic phase transition resolved by the measurement of magnetic susceptibility and lattice changes by XRD.

The intrinsic magnetic topological insulator MnBi 2 Te 4 has attracted significant interest recently as a promising platform for exploring exotic quantum phenomena. Here we report that, when atomically thin MnBi 2 Te 4 is deposited on a substrate such as silicon oxide or gold, there is a very strong mechanical coupling between the atomic layer and the supporting substrate. This is manifested as an intense low-frequency breathing Raman mode that is present even for monolayer MnBi 2 Te 4 . Interestingly, this coupling turns out to be stronger than the interlayer coupling between the MnBi 2 Te 4 atomic layers. We further found that these low-energy breathing modes are highly sensitive to sample degradation, and they become drastically weaker upon ambient air exposure. This is in contrast to the higher energy optical phonon modes which are much more robust, suggesting that the low-energy Raman modes found here can be an effective indicator of sample quality.

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