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MXenes are a large and new family of intrinsically magnetic two-dimensional (2D) transition-metal carbides and nitrides. This family has been adding new members since their first discovery in 2011, and has expanded with the exploring of ordered double transition-metal (DTM) MXenes. In this study, we have investigated the electronic and magnetic properties of thirteen bare and fourteen oxygen-terminated DTM MXene structures (M3C2, M3C2O2, MM'C2 and MM'C2O2, M = Ti, Zr, Cr, and Mo; M' = Ti, V, Nb, and Ta). The Hubbard-U parameter strongly depends on the atom environment and the coordination number in the cell. Therefore, for the first time in the literature, we have calculated the Hubbard-U parameters for each considered MXene structure systematically instead of taking them randomly. The investigated MXene structures have striking properties with respect to their magnetic ground states, and show ferromagnetic to antiferromagnetic or non-magnetic properties, accompanied by semiconductor to metallic or semi-metallic properties, depending on the transition metal(s) or termination by oxygen. We have performed Monte Carlo simulations to obtain the magnetic phase transition temperature of each structure. Additionally, coercivity and remanence values have been calculated for ferromagnetic cases, and we have investigated the hysteresis features of the MXenes of interest by applying a cyclic magnetic field at several temperatures.
RESUMEN
An experimental group (Angew. Chem., Int. Ed., 2021, 60, 7013-7017) has recently demonstrated the synthesis of two-dimensional (2D) RuSe2, which was shown to hold promise for hydrogen evolution due to enhanced HER performance. Herein, we studied the effects of external factors (strain, electric field, and atom adsorption) on the electronic and magnetic properties of T'-RuX2 (X = S, Se) sheets using DFT+U calculations. The estimated carrier effective mass results show that electrons are heavier than holes for T'-RuX2 sheets. The band-gap increases when the bi-axial strain increases from -5% to -1% (-5% to 1%) for T'-RuS2(RuSe2) and then decreases beyond these strain points. We found that the T'-RuX2 sheets exhibit a semiconductor to metal transition under a maximum electric field strength of 10 V nm-1. It is revealed that the magnetic moment can be achieved in T'-RuX2via adsorption of Li, Na, and K atoms. The findings show that the AFM state is the preferred magnetic ground state for T'-RuS2 with adsorbed Li and Na, whereas FM is the magnetic ground state for the remaining atm-RuX2 systems. Interestingly, an indirect to direct transition of the band-gap for T'-RuS2 with adsorbed K was found whereas the remaining T'-RuX2 with adsorbed Li, Na and K atoms showed either half-metallic or metallic electronic properties. Our results can extend the application of T'-RuX2 sheets in actuating, optoelectronic and spintronic fields.
RESUMEN
Transition metal boro-carbide (TM2BC) structures crystallize in the layered orthorhombic structure in their bulk phases. In this study, however, we find that TM2BC (TM = Cr, Mn) prefer a tetragonal (t) crystal structure in their monolayer phases due to the occurrence of strong sp2 bonds between the metal and B/C atoms instead of sp3 + sp2 bonds which exist in the orthorhombic phase. The calculated energy difference between the orthorhombic and the tetragonal structures based on density functional theory (DFT) is more than 1 eV per unit cell. In addition, t-Cr2BC and t-Mn2BC monolayers are dynamically and thermally stable with their magnetic metal electronic structures. For further investigations, we combine our DFT calculations with the Monte Carlo simulations and find that both t-TM2BC monolayers show ferromagnetic properties. The calculated Curie temperatures are 846 K and 128 K for t-Cr2BC and t-MnBC sheets, respectively. In addition, we examine the magnetic anisotropy energies (MAE) of t-TM2BC monolayers and find that both structures prefer out-of-plane as the easy axis magnetization direction and the applied electric field can easily modulate the MAE of the monolayers. Our theoretical calculations reveal that t-TM2BC (TM = Cr, Mn) sheets have great potential for the future design of controllable spintronic devices with their tunable MAE properties.
RESUMEN
Porous nanosheet materials have recently emerged as attractive candidates to serve as nanofiltration membranes. Through first-principles calculations based on density functional theory (DFT) calculations, we propose a new porous dodecagonal GeC (d-GeC) monolayer. We show that the d-GeC monolayer exhibits excellent energetic, mechanical, dynamic, and thermal stabilities. The d-GeC monolayer shows semiconducting properties with an indirect band gap of 1.73 eV (2.53 eV) PBE(HSE06). We also show that the d-GeC monolayer can serve as a good membrane for molecular and atomic permeation due to its low value of estimated diffusion energy barriers. Our results demonstrate the potential of the d-GeC monolayer for the design of nanofiltration membrane technology.
RESUMEN
Two-dimensional (2D) transition metal boron-carbide is a novel material that has unique properties suitable for advanced spintronics and storage applications. Through first-principles calculations based on density functional theory (DFT) calculations, we report a new class of stable 2D ceramic WXBC (X = W, Mn, Fe) monolayers. We find that all WXBC monolayers prefer a ferromagnetic ground state with metallic electronic property. DFT calculations proved that WXBC monolayers exhibit good energetic, mechanical, and dynamic stabilities. More importantly, these monolayers exhibit large magnetic anisotropy energy (MAE) of 1213 µeV, 247 µeV and 20 µeV per magnetic atom for W2BC, WMnBC, and WFeBC, respectively. An out-of-plane easy axis (EA) magnetization direction is found for W2BC whereas the EA for WMnBC and WFeBC are in-plane. By performing Monte Carlo (MC) simulations based on the 2D Heisenberg model, we predict Curie temperatures (T C) of 155 K for the W2BC monolayer. The Berezinskii-Kosterlitz-Thouless transition (BKT) temperature values of WMnBC and WFeBC are as high as 374.69 K and 417.39 K. For further investigations, the adsorption properties of Li, Na, and K atoms on WXBC (atm-WXBC) systems are examined. It is revealed that the initial ferromagnetic metallic properties of bare WXBC monolayers are maintained for all atm-WXBC systems. The obtained strong chemisorption energies are high enough to make adsorbed Li, Na, and K immobile on WXBC surfaces. All these findings demonstrate the unique potential of WXBC monolayers as multifunctional candidates for advanced magnetic device and storage applications.
RESUMEN
A recent theoretical work predicted the orthorhombic phase of the V2P2 sheet with the half-metallic electronic property using a linear combination of atomic orbitals (LCAO) basis set based on density functional theory (DFT). However, in the plane-wave DFT method, the tetragonal (t) V2P2 phase is the ground state structure. The total energy of the optimized tetragonal V2P2 is 0.91 eV per cell lower than that of the orthorhombic phase. Herein, we investigated the effects of Hubbard U correction onthe electronic, magnetic, and adsorption properties of the t-V2P2 sheet. The t-V2P2 sheet is found to be dynamically and mechanically stable. The t-V2P2 sheet prefers an antiferromagnetic ground state with an indirect narrowed bandgap of 0.23 eV. The estimated electron mobility in the t-V2P2 sheet at room temperature is approximately 24 times that of a hole. The t-V2P2 sheet exhibits a sizable magnetic anisotropy (MAE) of 69.63 µeV per V atom with in-plane magnetization. Mean-field approximation based on the 2D classical Heisenberg model predicts a high Néel temperature (T N) of the t-V2P2 sheet up to 1263 K. The Li atom adsorption on the t-V2P2 sheet shows a transition from semiconductor to metal. Also the Li-V2P2 system has a residual integer magnetic moment of 1 µ B. Due to strong steric coulomb repulsion, the minimum diffusion energy barrier (E a) for the Li-ion on the t-V2P2 surface is high enough to make the Li atom immobile. Our findings demonstrate the potential of the t-V2P2 sheet for antiferromagnetic spintronics and sensing applications.