The two-dimensional van der Waals (vdW) magnets retaining magnetic order in atomically thin limit demonstrate challenging physical phenomena and they are considered as prospective building blocks for construction of advanced spintronics and nanoelectronics devices. Here, we present experimental evidence for negative thermal expansion of lattice volume and vdW layers and strong spin–phonon coupling effects, caused by formation of the long-range ferromagnetic order in the vdW material CrBr₃. The neutron and X-ray diffraction measurements revealed anomalous temperature variation of lattice parameters and interatomic distances and angles in the vicinity of Curie temperature (T_C). A pronounced rise of the frequencies of the most of the observed vibrational modes and unusual reversal broadening of their full widths at half maximum below T_C was found from Raman spectroscopy measurements.

Due to their high refractive index, record optical anisotropy and a set of excitonic transitions in visible range at a room temperature, transition metal dichalcogenides have gained much attention. Here, we adapted a femtosecond laser ablation for the synthesis of WSe₂ nanoparticles (NPs) with diameters from 5 to 150 nm, which conserve the crystalline structure of the original bulk crystal. This method was chosen due to its inherently substrate-additive-free nature and a high output level. The obtained nanoparticles absorb light stronger than the bulk crystal thanks to the local field enhancement, and they have a much higher photothermal conversion than conventional Si nanospheres. The highly mobile colloidal state of produced NPs makes them flexible for further application-dependent manipulations, which we demonstrated by creating substrates for SERS sensors.

The crystal structure and vibration spectra of sodium niobate NaNbO₃ have been studied by means of neutron diffraction, X-ray diffraction and Raman spectroscopy at high pressures. An isostructural phase transformation from the initial antiferroelectric phase to an intermediate antiferroelectric phase HP-I have been observed under 2 GPa. This transformation is caused by complex reorientations of NbO₆ octahedra. Subsequent structural phase transition from the phase HP-I to an orthorhombic phase HP-III have been detected at pressures above 10 GPa. This transition leads to suppression of an antiferroelectric state of NaNbO₃. The observed phase transitions are accompanied by anomalies in lattice parameters compression.

The magnetic La _1-x Sr _x MnO ₃ particles of ≈50 nm size have been prepared in the flux of sodium nitrite at ≈500°C. A detailed magnetic study, including the neutron diffraction at zero and high pressures, has been performed on compositions x = 0.28 and 0.37, as well as on comparative samples prepared via sol-gel route. Based on these experiments, we conclude that the molten salt prepared particles show significant oxygen excess δ > 0 that can be ascribed mainly to the surface oxygen chemisorption. As a consequence, the valence of Mn ions is shifted toward a higher oxidation state, and this shift probably exhibits a pronounced radial distribution in the particles, reaching possibly pure Mn ⁴⁺ at the uppermost surface layer. We suggest that such overdoping is an additional reason for magnetically dead shell in manganite nanoparticles and is also the source of surface stress that compresses the particle core and modifies its physical properties. Such compressive stress drives the magnetic ground state of the composition x = 0.37 toward a mixture of ferromagnetic (FM) and A-type anti-FM (AFM) ordering. Although the surface effects should also occur in the particles with x = 0.28, the AFM phase is practically absent in this sample but can be induced by high pressure.