Impact of Coulomb Correlations on Magnetic Anisotropy in Mn3Ga Ferrimagnet.

Traditional density functional theory (DFT) miserably fails to reproduce the experimental volume and magnetic anisotropy of D022 Mn3Ga, which has recently become one of the most sought-after materials in order to achieve a stable spin switching at low current density. Despite great progress over the last 10 years, this issue has hitherto remained unsolved. Here, taking into account the effects of strong electronic correlations beyond what is included in standard DFT, we show by comparison with the experiment that the DFT+U method is capable of quantitatively describing the volume and the magnetic anisotropy energy (MAE) in this alloy with physically meaningful choice of onsite Coulomb-U parameter. For the first time using a plane-wave code, we decompose MAE into spin channel-resolved components in order to determine spin-flip and spin-conserving contributions. The Mn atom at the tetrahedral site is identified as the primary source of the high perpendicular MAE with the most dominant spin-orbit coupling (SOC) occurring between its two orbital pairs: ↑↑ coupling and ↓↓ coupling between [Formula: see text] and d xy , and ↑↓ coupling between d yz and [Formula: see text]. Using the SOC-perturbation theory model, we provide interpretation of our numerical results. These results are important for quantitative microscopic understanding of the large perpendicular MAE observed in this material, and should assist in harnessing its potential for applications in futuristic spintronic devices.

Visualizing Non-abrupt Transition of Quantum Well States at Stepped Silver Surfaces.

We use scanning tunneling spectroscopy (STS) experiments and first-principles density functional theory (DFT) calculations to address a fundamental question of how quantum well (QW) states for electrons in a metal evolve spatially in the lateral direction when there is a surface step that changes the vertical confinement thickness. This study reveals a clear spatially dependent, nearly continuous trend in the energetic shifts of quantum well (QW) states of thin Ag(111) film grown on Cu(111) substrate, showing the strongest change near the step edge. A large energetic shift equaling up to ~200 meV with a lateral extension of the QW states of the order of ~20 Å is found, even though the step-edge is atomically sharp as evidenced by a line scan. The observed lateral extension and the nearly smooth transition of QW states are understood within the context of step-induced charge oscillation, and Smoluchowski-type charge spreading and smoothing.

Role of dynamical instability in the ab initio phase diagram of calcium.

In the 32-119 GPa pressure range and at room temperature, a simple cubic phase was reported for calcium in many different experiments. Standard linear response theory, both within density functional perturbation theory and frozen phonon calculations, presents dynamical instabilities for the simple cubic structure in the whole pressure range. Many other possible candidate phases, as well as several possible stabilization mechanisms for the simple cubic phase, have been proposed as the result of ab initio predictions but the role of temperature on the relative stability of the different phases has not been systematically investigated. We revisit the stability of the three most important candidate phases of calcium for the intermediate pressure range and for various temperatures, taking explicitly into account thermal corrections relative to electronic as well as phononic entropy and anharmonic contributions. This corrects the discrepancies among previous theoretical results and experiments and presents a different picture of the temperature driven phase transition, which results from dynamical anharmonic stabilization of simple cubic and destabilization of the tetragonal phase.