RESUMO
Density functional theory (DFT) calculations are performed to predict the structural, electronic and magnetic properties of electrically neutral or charged few-atomic-layer (AL) oxides based on polar perovskite KTaO3. Their properties vary greatly with the number of ALs (nAL) and the stoichiometric ratio. In the few-AL limit (nAL ≤ 14), the even AL (EL) systems with the chemical formula (KTaO3)n are semiconductors, while the odd AL (OL) systems with the formula Kn+1TanO3n+1 or KnTan+1O3n+2 are half-metal except for the unique KTa2O5 case which is a semiconductor due to the large Peierls distortions. After reaching a certain critical thickness (nAL > 14), the EL systems show ferromagnetic surface states, while ferromagnetism disappears in the OL systems. These predictions from fundamental complexity of polar perovskite when approaching the two-dimensional (2D) limit may be helpful for interpreting experimental observations later.
RESUMO
Due to the lack of inversion symmetry and the discovery of room-temperature ferromagnetism, two-dimensional semiconducting vanadium-based van der Waals transition-metal dichalcogenides (V-TMDs) are drawing attention for their possible application in spintronics and valleytronics. Here, we show the functional properties enriched by the broken inversion, out-of-plane mirror, and time-reversal symmetries of Janus H-VXY TMDs (X, Y = S, Se, Te). By first-principles calculations, we reveal the intrinsic xy easy-plane magnetism of the Janus vanadium-based TMD monolayers and systematically study their hidden valley polarization and giant magneto band structure. Their strong nearest-neighbor exchange strengths lead to near-room-temperature magnetic phase transitions. The Janus H-VXY system also exhibits piezoelectricity with nonzero e31 and e21. Interestingly, it is found that the right-handed Dzyaloshinskii-Moriya interaction has nonzero in-plane components in our Janus system, with fluctuating magnitudes determined by competence between relaxed bond-angle and atomic index of ligands.
RESUMO
Two-dimensional (2D) transition metal oxide monolayers are currently attracting great interest in materials research due to their versatility and tunable electronic and magnetic properties. In this study, we report the prediction of magnetic phase changes in HxCrO2(0 ⩽x⩽ 2) monolayer on the basis of first-principles calculations. As the H adsorption concentrationxincreases from 0 to 0.75, HxCrO2monolayer transforms from a ferromagnetic (FM) half-metal to a small-gap FM insulator. Whenx= 1.00 and 1.25, it behaves as a bipolar antiferromagnetic (AFM) insulator, and eventually becomes an AFM insulator asxincreases further up to 2.00. The results suggest that the magnetic properties of CrO2monolayer can be effectively controlled by hydrogenation, and that HxCrO2monolayers have the potential for realizing tunable 2D magnetic materials. Our results provide a comprehensive understanding of the hydrogenated 2D transition metal CrO2and provide a research method that can be used as a reference for the hydrogenation of other similar 2D materials.
RESUMO
Density functional theory calculations were performed for the electronic and the ferroelectric properties of the bulk and the monolayer benzylammonium lead-halide (BA2PbCl4). Our calculations indicate that both the bulk and monolayer systems display a band gap of â¼3.3 eV (HSE06+SOC) and a spontaneous polarization of â¼5.4 µC/cm2. The similar physical properties of bulk and monolayer systems suggest a strong decoupling among the layers in this hybrid organic-inorganic perovskite. Both the ferroelectricity, through associated structure distortion, and the spin-orbit coupling, through splitting induced in the electronic bands, significantly influence the band gaps. Most importantly, we found for the first time in a two-dimensional hybrid organic-inorganic class of material, a peculiar spin texture topology such as a unidirectional spin-orbit field, which may lead to a protection against spin decoherence.