Browsing by Author "Kadioglu, Y."
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Item Open Access Columnar antiferromagnetic order of a MBene monolayer(American Physical Society, 2021-04-16) Ozdemir, I.; Kadioglu, Y.; Yüksel, Y.; Akıncı, Ü.; Üzengi Aktürk, O.; Aktürk, E.; Çıracı, SalimFirst-principles density functional theory, combined with the Monte Carlo method, predicts that the Fe2B2 monolayer of the MBene family has a stable columnar antiferromagnetic (AFM) ground state. Below the critical temperature, Tc=115 K in equilibrium, the spins rotate by the same amount in every other column of Fe atoms, but they retain the same direction in the same column. Under applied tensile strains, Tc and the order parameter can increase nonmonotonically. The onset of the columnar order can result in a transition from two dimension (2D) to 1D in magnetic, electronic, and conduction properties. The ordered magnetic state itself can be tuned by external magnetic field, whereby the columnar magnetic order changes to ferromagnetic order with a double hysteresis behavior. When terminated by Fluorine atoms, the columnar order changes to the AFM order with Tc rising above room temperature. This situation is rather unusual and insofar is fundamental for a realistic, strictly 2D monolayer and can have critical consequences in spin conduction.Item Open Access Functionalization of single-layer nitrogene by vacancy, adatoms, and molecules(American Chemical Society, 2017-02) Kadioglu, Y.; Ü. Aktürk, O.; Aktürk, E.; Çıracı, SalimDespite its strong N2 molecule, recent studies have shown that nitrogen, the lightest group V element, remains stable in the free-standing, single-layer buckled honeycomb structure with two-dimensional (2D) hexagonal lattice. This structure is called nitrogene and is predicted to be a nonmagnetic, wide band gap semiconductor or insulator. In this paper, we investigated the formation of a single vacancy, as well as the adsorption of selected single adatoms and molecules on 2D nitrogene, using the supercell method within the density functional theory. Through the consideration of large supercells, the couplings between adjacent vacancies and adspecies are minimized; hence, the results are taken to represent single, isolated defect and adspecies. We found that a single vacancy contributes a local magnetic moment and filled and empty localized gap states at low temperature but is prone to instability due to thermal excitations. Adatoms are bound to the surface of nitrogene and form localized gap states contributing a diversity of electronic and magnetic properties. Adsorption of adatoms, such as B, C, Si, and N, however, give rise to local and strong reconstruction in nitrogene in their close proximity. Notably, a N adatom forms a strong N2 molecule by removing one N atom from nitrogene and leaves a vacancy behind. Conversely, the interactions between selected molecules, such as H2, O2, H2O, and N2, and the surface of nitrogene are rather weak and do not induce any change in the physical properties. However, H2 and O2 can be dissociated at the edges of a nitrogene flake and concomitantly can remove host N atoms to form NH2 and NO2 molecules. Calculated properties of adatoms adsorbed to nitrogene differ dramatically from the properties of those adsorbed to single-layer structures of other group V elements.Item Open Access Modification of electronic structure, magnetic structure, and topological phase of bismuthene by point defects(American Physical Society, 2017) Kadioglu, Y.; Kilic, S. B.; Demirci, S.; Aktürk, O. Ü.; Aktürk, E.; Çıracı, SalimThis paper reveals how the electronic structure, magnetic structure, and topological phase of two-dimensional (2D), single-layer structures of bismuth are modified by point defects. We first showed that a free-standing, single-layer, hexagonal structure of bismuth, named h-bismuthene, exhibits nontrivial band topology. We then investigated interactions between single foreign adatoms and bismuthene structures, which comprise stability, bonding, electronic structure, and magnetic structures. Localized states in diverse locations of the band gap and resonant states in band continua of bismuthene are induced upon the adsorption of different adatoms, which modify electronic and magnetic properties. Specific adatoms result in reconstruction around the adsorption site. Single vacancies and divacancies can form readily in bismuthene structures and remain stable at high temperatures. Through rebondings, Stone-Whales-type defects are constructed by divacancies, which transform into a large hole at high temperature. Like adsorbed adatoms, vacancies induce also localized gap states, which can be eliminated through rebondings in divacancies. We also showed that not only the optical and magnetic properties, but also the topological features of pristine h-bismuthene can be modified by point defects. The modification of the topological features depends on the energies of localized states and also on the strength of coupling between point defects. © 2017 American Physical Society.