Minho Lee

Ferroelectric control of magnetic anisotropy of FePt/BaTiO3 magnetoelectric heterojunction: A density functional theory study

Using ab-initio simulations, we investigated the effects of ferroelectric polarization on the magnetic anisotropy of FePt/BaTiO3 heterojunctions. The changed electronic structure at the interface of FePt and BaTiO3 reduced the magnetic anisotropy energy (MAE) under ferroelectric polarization. Through the electronic density of states analysis, it was found that the MAE change is mainly due to the changed hybridization state between d-orbitals of interface Ti and Fe atoms.

Geometric and magnetic properties of Co adatom decorated nitrogen-doped graphene

The potential for nitrogen doped graphene with dispersed Co metal atoms as a candidate material for future spintronic applications was studied using first-principles calculations. Among the three types of defective structures, the pyridinic and pyrrolic systems were demonstrated to be structurally stable since the binding energy between the Co adatom and these substrate layers exceeded the cohesive energy of Co metal alone. Also, Co adatom on these two structures showed high magnetic moment values, which surpassed that of the Co metal bulk. From these results, it is shown that the pyridinic and pyrrolic N defects on graphene have a positive effect on the geometric stability and magnetic property of decorated Co atoms.

Oxygen Vacancy Chain Formation in TiO2 under External Strain for Resistive Switching Memory

The electronic structure and vacancy formation energy of rutile TiO2 with ordered oxygen vacancies were calculated using the density functional theory with on-site Coulomb corrections between Ti 3d orbital and O 2p orbital (LDA+Ud+Up). The calculated band gaps are about 3 eV, using LDA+Ud+Up, and a hybrid functional proposed by Heyd–Scuseria–Ernzerhog. The ordered oxygen vacancies were introduced along the [001] direction within a 3×3×4 supercell of rutile TiO2-x that consisted of 72 Ti and 136 O atoms. Biaxial strain was induced in the rutile TiO2 along the x- and y-directions up to ±5%. The lowest formation energy of ordered oxygen vacancies was found in 5% compressive strain and deemed as a thermodynamically favorable structure.

Magnetic Properties of Iron on Strained Graphene: Density Functional Theory Study

Using ab initio calculations, we investigated the effects of strains on the magnetic properties of Fe/graphene heterojunctions. The changed electronic structures of Fe layer by contacting graphene sheet reduced the magnetic anisotropy and increased the magnetic moment of Fe layer. Through the analysis of the electronic density of states of decomposed Fe 3d orbitals and C 2pz orbital, we found that the 3dyz, 3dzx, and 3dz2 orbitals are attributed to the changed magnetic moment and magnetic anisotropy of Fe/graphene by biaxial strain.

Configuration Dependency of Attached Epoxy Groups on Graphene Oxide Reduction: A Molecular Dynamics Simulation

The atomic behavior of epoxy groups on a graphene oxide sheet was observed during high thermal heat annealing using a reactive force-field based on molecular dynamics simulations. We found the oxygen-containing functional groups interplay with each other and desorbed from the graphene oxide sheet by a form of O2 gas if they were initially in close distance. Through comparing reduction results of graphene oxide with different densities of the nearest neighboring epoxy pairs, we confirmed that the amount of released O2 gas has a clear tendency to increase with a higher density of epoxy pairs in close distance on a graphene oxide sheet.