Browsing by Author "Wang, Wei-Hua"
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Item D-Type Anti-Ferromagnetic Ground State in Ca₂Mn₂O₅(IOP Publishing Ltd, 2017-02) Liu, Pan; Wang, Wei-Hua; Wang, Weichao; Cheng, Ya-Hui; Lu, Feng; Liu, Hui; Wang, WeichaoWe study the electronic and magnetic properties of an oxygen-deficient perovskite Ca₂Mn₂O₅ based on the first principle calculations. The calculations show that the ground state of Ca₂Mn₂O₅ is a D-type anti-ferromagnetic structure with the anti-ferromagnetic spin coupling along the c-direction. The corresponding electronic structure of the D-type state is investigated, and the results display that Ca₂Mn₂O₅ is an insulator with an indirect energy gap of ~2.08 eV. By the partial density-of-state analysis, the valence band maximum is mainly contributed to by the O-2p orbitals and the conduction band minimum is contributed to by the O-2p and Mn-3d orbitals. Due to the Coulomb repulsion interaction between electrons, the density of state of Mn-3d is pulled to -6--4.5 eV. .Item Electronic Structure and Ferromagnetism Modulation in Cu/Cu₂O Interface: Impact of Interfacial Cu Vacancy and Its Diffusion(Nature Publishing Group) Li, Hao-Bo; Wang, Weichao; Xie, Xinjian; Cheng, Yahui; Zhang, Zhaofu; Dong, Hong; Zheng, Rongkun; Wang, Wei-Hua; Lu, Feng; Liu, Hui; Wang, WeichaoCu/Cu₂O composite structures have been discovered to show sizable ferromagnetism (FM) with the potential applications in spintronic devices. To date, there is no consensus on the FM origin in Cu/Cu₂O systems. Here, first principles calculations are performed on the interface structure to explore the microscopic mechanism of the FM. It is found that only the Cu vacancy (VCu) adjacent to the outermost Cu₂O layer induces a considerable magnetic moment, mostly contributed by 2p orbitals of the nearest-neighbor oxygen atom (O_(NN)) with two dangling bonds and 3d orbitals of the Cu atoms bonding with the (O_(NN)). Meanwhile, the charge transfer from Cu to Cu₂O creates higher density of states at the Fermi level and subsequently leads to the spontaneous FM. Furthermore, the FM could be modulated by the amount of interfacial VCu, governed by the interfacial Cu diffusion with a moderate energy barrier (~1.2 eV). These findings provide insights into the FM mechanism and tuning the FM via interfacial cation diffusion in the Cu/Cu₂O contact.Item First-Principle Prediction on STM Tip Manipulation of Ti Adatom on Two-Dimensional Monolayer YBr₃(Wiley-Hindawi, 2019-02-04) Liu, Pan; Wu, Maokun; Liu, Hui; Lu, Feng; Wang, Wei-Hua; Cho, Kyeongjae; 0000-0003-2698-7774 (Cho, K); 369148996084659752200 (Cho, K); Cho, KyeongjaeScanning tunneling microscopy (STM) is an important tool in surface science on atomic scale characterization and manipulation. In this work, Ti adatom manipulation is theoretically simulated by using a tungsten tip (W-tip) in STM based on first-principle calculations. The results demonstrate the possibility of inserting Ti adatoms into the atomic pores of monolayer YBr₃, which is thermodynamically stable at room temperature. In this process, the energy barriers of vertical and lateral movements of Ti are 0.38eV and 0.64eV, respectively, and the Ti atoms are stably placed within YBr₃ by >1.2eV binding energy. These theoretical predictions provide an insight that it is experimentally promising to manipulate Ti adatom and form artificially designed 2D magnetic materials.