49 research outputs found
Variation of magnetic properties of SrFeMoO due to oxygen vacancies
Oxygen vacancies can be of utmost importance for improving or deteriorating
physical properties of oxide materials. Here, we studied from first-principles
the electronic and magnetic properties of oxygen vacancies in the double
perovskite SrFeMoO (SFMO). We show that oxygen vacancies can increase
the Curie temperature in SFMO, although the total magnetic moment is reduced at
the same time. We found also that the experimentally observed valence change of
the Fe ions from to in the x-ray magnetic circular dichroism (XMCD)
measurements is better explained by oxygen vacancies than by the assumed mixed
valence state. The agreement of the calculated x-ray absorption spectra and
XMCD results with experimental data is considerably improved by inclusion of
oxygen vacancies.Comment: submitted to PRB but rejected, major revision, submitting to JPC
First-principles investigations of the magnetic phase diagram of GdCaMnO
We studied for the first time the magnetic phase diagram of the rare-earth
manganites series GdCaMnO (GCMO) over the full
concentration range based on density functional theory. GCMO has been shown to
form solid solutions. We take into account this disordered character by
adapting special quasi random structures at different concentration steps. The
magnetic phase diagram is mainly described by means of the magnetic exchange
interactions between the Mn sites and Monte Carlo simulations were performed to
estimate the corresponding transition temperatures. They agree very well with
recent experiments. The hole doped region shows a strong ferromagnetic
ground state, which competes with A-type antiferromagnetism at higher Ca
concentrations .Comment: Submitted to PR
Exchange-Correlation Catastrophe in Cu-Au: A Challenge for Semilocal Density Functional Approximations
Gradient-level and nonlocal density functional descriptions of Cu-Au intermetallic compounds
We use three gradient level and two nonlocal density functional approximations to study the thermodynamic properties of Cu-Au compounds. It is found that a well-designed gradient level approximation (quasi non-uniform approximation, QNA) reproduces the experimental equilibrium volumes and the formation energies of L12 and L10 phases. On the other hand, QNA predicts a non-existent beta(2) phase, which can be remedied only when employing the nonlocal hybrid-level Heyd-Scuseria-Ernzerhof (HSE06) or Perdew-Burke-Ernzerhof (PBE0) approximations. Gradient-level approximations lead to similar electronic structures for the Cu-Au compounds whereas hybrids shift the d-band towards negative energies and account for the complex d-d hybridization more accurately
Interatomic Fe-Cr potential for modeling kinetics on Fe surfaces
To enable accurate molecular dynamics simulations of iron-chromium alloys with surfaces, we develop, based on density-functional-theory (DFT) calculations, a new interatomic Fe-Cr potential in the Tersoff formalism. Contrary to previous potential models, which have been designed for bulk Fe-Cr, we extend our potential fitting database to include not only conventional bulk properties but also surface-segregation energies of Cr in bcc Fe. In terms of reproducing our DFT results for the bulk properties, the new potential is found to be superior to the previously developed Tersoff potential and competitive with the concentration-dependent and two-band embedded-atom-method potentials. For Cr segregation toward the (100) surface of an Fe-Cr alloy, only the new potential agrees with our DFT calculations in predicting preferential segregation of Cr to the topmost surface layer, instead of the second layer preferred by the other potentials. We expect this rectification to foster future research, e.g., on the mechanisms of corrosion resistance of stainless steels at the atomic level.Peer reviewe