Determination of Perpendicular Magnetic Anisotropy in Fe/MgO/Fe Magnetic Tunnel Junction: A DFT-Based Spin-Orbit Torque Approach

In our JunPy package, we have successfully combined the self-consistent Hamiltonian from first-principles calculations with the nonequilibrium Green's function method to calculate the noncollinear spin torque in the nm-scale magnetic heterojunctions. The spin-orbit coupling within the first-principles calculations is included to determine the magnetic anisotropy (MA) of an Fe/MgO/Fe magnetic tunnel junction (MTJ) with a spin-orbit torque (SOT) method. The angular dependence of accumulative SOT indicates the biaxial and uniaxial MA corresponding to the in-plane and out-of-plane rotations of the free magnetization, respectively. Our results agree with the conventional MA energy calculation for a whole MTJ and provide insights into micro-spin dynamics of local magnetic moments.Comment: 11 pages, 4 figure

MoSe2 nanosheets and their graphene hybrids: synthesis, characterization and hydrogen evolution reaction studies

MoSe2 nanosheets and MoSe2/graphene hybrids have been prepared by a facile hydrothermal method. The number of layers of the MoSe2 nanosheets is typically <10 as confirmed directly by transmission electron microscopy and indirectly by a red shift of the characteristic A(1g) Raman peak. The hydrogen evolution reaction ( HER) studies show that the onset potentials of MoSe2 and MoSe2/RGO hybrids are only similar to 0.15 V vs. RHE and similar to 0.05 V vs. RHE, respectively, about 20-30 mV lower than those of MoS2 and its graphene hybrids reported previously. Density functional theory calculations reveal that the Gibbs free energy for atomic hydrogen adsorption (Delta G(H)(0)) on MoSe2 edges is closer to thermoneutral than that on MoS2, with an H coverage of about 75% on the edge under operating conditions, which is also higher than that of MoS2 reported in the literature. The consistency between the experimental and computational results indicates that MoSe2 nanosheets have potential to be a better HER catalyst than their MoS2 counterpart

Stepwise Evolution of Photocatalytic Spinel-Structured (Co,Cr,Fe,Mn,Ni)3O4 High Entropy Oxides from First-Principles Calculations to Machine Learning

High entropy oxides (HEOx) are novel materials, which increase the potential application in the fields of energy and catalysis. However, a series of HEOx is too novel to evaluate the synthesis properties, including formation and fundamental properties. Combining first-principles calculations with machine learning (ML) techniques, we predict the lattice constants and formation energies of spinel-structured photocatalytic HEOx, (Co,Cr,Fe,Mn,Ni)3O4, for stoichiometric and non-stoichiometric structures. The effects of site occupation by different metal cations in the spinel structure are obtained through first-principles calculations and ML predictions. Our predicted results show that the lattice constants of these spinel-structured oxides are composition-dependent and that the formation energies of those oxides containing Cr atoms are low. The computing time and computing energy can be greatly economized through the tandem approach of first-principles calculations and ML

Hydrogen Evolution Driven by Photoexcited Entangled Skyrmion on Perovskite Ca2Nan–3NbnO3n+1 Nanosheet

A magnetic skyrmion is a topologically stable state with potential applications for realizing the next-generation spintronic devices. Here, we demonstrate the real-space observation of skyrmions in Dion−Jacobson phase perovskite, Ca2Nan−3NbnO3n+1− (CNNO), nanosheets by using optical injection. The CNNO4 and CNNO6 nanosheets exhibit weak ferromagnetics, while the CNNO5 nanosheet is superparamagnetic. The magnetic skyrmion can be clearly observed in those 2D nanosheets in the absence of the external magnetic field. First-principles calculations and micromagnetic simulations predict that the magnetic skyrmions in CNNO nanosheets is Neel-type with a diameter of 11−15 nm, in corresponding to the experiments. Our findings provide insights for developing room-temperature skyrmions in CNNO nanosheets for skyrmionic water-splitting performance in future energy generation and quantum computing devices

Dion–Jacobson Phase Perovskite Ca2Nan–3NbnO3n+1– (n = 4–6) Nanosheets as High-κ Photovoltaic Electrode Materials in a Solar Water-Splitting Cell

A well-crystalline two-dimensional (2D) perovskite material, Ca2Nan−3NbnO3n+1− (CNNO−) nanosheets, derived from the Dion−Jacobson phase has the potential to generate hydrogen through photoelectrochemical water splitting. Here, we demonstrate that a high-κ photovoltaic electrode consisting of CNNO− nanosheets with layer number n = 4−6 and a hole-transport polymer, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), can form a p−n junction and an overall solar-to-hydrogen water-splitting cell, with the highest efficiency of 0.52% and a hydrogen evolution rate of 80.64 μmol h−1. First-principles calculations are carried out to confirm the energy-band diagram of this promising material, which significantly affects the electronic transition process in a solar water-splitting cell. 2D CNNO− nanosheets present great potential for serving as nanoelectronic water-splitting devices in single transistors