[en] We have calculated the phase diagram of the symmetric one-dimensional Anderson lattice using the local mean-field method, which can reveal the basic properties of the system throughout the entire parameter space. Near quarter and half filling the antiferromagnetic phase is the ground state. For intermediate band filling there is a continuous second-order phase transition to a ferromagnetic state. At quarter filling there is a transition from a metallic paramagnetic state to an insulating antiferromagnetic state as the on-site Coulomb interaction increases. [copyright] 2001 American Institute of Physics

[en] Dislocation core properties of Al with and without H impurities are studied using the Peierls-Nabarro model with parameters determined by ab initio calculations. We find that H not only facilitates dislocation emission from the crack tip but also enhances dislocation mobility dramatically, leading to macroscopically softening and thinning of the material ahead of the crack tip. We observe strong binding between H and dislocation cores, with the binding energy depending on dislocation character. This dependence can directly affect the mechanical properties of Al by inhibiting dislocation cross-slip and developing slip planarity

[en] Employing ab initio electronic structure calculations we have investigated the magnetostrictive properties and the effect of epitaxial strain on the magnetic anisotropy (MA) of Au/FeCo/MgO heterostructure. Under small expansive strain on the FeCo layer the system exhibits an in-plane MA. The calculations reveal that the strain dependence of the MA is nonlinear and that the FeCo film undergoes a spin reorientation at a critical strain between 2 and 4%. The underlying mechanism is the strain-induced shift of the spin–orbit coupled d-states of the Fe atoms. We predict a giant magnetostriction coefficient of about 420×10"−"6 in the heterostructure. - Highlights: • Nonlinear strain dependence of magnetic anisotropy. • The FeCo film undergoes a spin reorientation at a critical strain between 2 and 4%. • The underlying mechanism is the strain-induced shift of the spin–orbit coupled d-states of the Fe atoms. • Giant magnetostriction coefficient of about 420×10"-"6 in the heterostructure.

[en] A quantum statistical theory of the influence of grain size on the residual extraordinary Hall effect (EHE) in magnetic metal-insulator granular alloys is presented. It is shown that under certain conditions the quasi-classical size-effect (QSE) can lead to similar behaviors of EHE in metal-metal and metal-insulator alloys. The possible dependences of EHE coefficient on the grain size and the role of the QSE in the giant EHE in nanocomposites are discussed

[en] Employing ab initio calculations we have determined the structural parameters of the paraelectric and ferroelectric phases of KH₂PO₄, which are in good agreement with experiment. The calculations reveal that the O-O bond length and the coordinated motion of the P and K atoms have a large effect on the double-well potential for H, controlling the distance, δ, between the two equilibrium positions of the H along the O-O bond in the paraelectric phase. The calculations provide new evidence that the ferroelectric phase transition in H-bonded crystals has also a displacive feature. (author). Letter-to-the-editor

[en] We report ab initio electronic structure calculations to study the effect of Ta cap on the magnetic properties and the magnetoelectric response of Ta/FeRh/MgO nanojunctions. The calculations reveal that the Ta cap reverses the magnetic phase stability in ultrathin FeRh films leading to the stabilization of the ferromagnetic phase and interfacial reconstructed ferromagnetism. We demonstrate that the Ta cap induces a large charge transfer which in turn reduces dramatically the magnetic moments of the interfacial Fe atoms regardless the magnetic configuration and enhances the in-plane (out-of-plane) magnetization orientation of the antiferromagnetic (AFM) (ferromagnetic (FM)) phase compared to the uncapped bilayer. The Ta cap modifies substantially and enhances the magnetoelectric response under an external electric field, where the voltage controlled magnetic anisotropy (VCMA) changes from $\vee$-shape in the AFM to linear behavior in the FM phase with large VCMA efficiency. These findings demonstrate the manipulation of magnetic ordering of FeRh films with heavy metal capping and electric field which can promote the application of FeRh alloy in MeRAM.

[en] Ab initio electronic structure calculations are employed to study the stability and mobility of mono-self interstitial atoms (SIA) in α-Fe under external deformation. The ab initio results indicate that the volumetric and uniaxial strain dependences of the SIA formation energy are different in the expansion and compression regimes, in contrast to the linear behavior in continuum elasticity theory. We find a <111>→<100> SIA reorientation mechanism induced by uniaxial expansion which proceeds via <11x>|_x=2.7 configuration. Volumetric and uniaxial deformations are also found to have a considerable influence on the migration paths and activation energy barriers for the <110>(110)↔<100>(100) transformation and the <111>↔<100> reorientation. The results reveal that (i) the volumetric expansion (compression) decreases (increases) substantially the migration energy barrier and renders the diffusion process three (one) dimensional, (ii) the uniaxial strain removes (decreases) the migration energy barrier for the <111>→<11x>|_x=2.7(<11x>|_x=2.7→<100>) transformation, leading to spontaneous reorientation of the <111> SIA, and (iii) the uniaxial deformation breaks the cubic symmetry of the system and in turn induces anisotropy of the migration rates along different directions. These calculations demonstrate that changes in the electronic structure induced by global elastic deformation lead to additional contributions to the formation and migration energies, which cannot be adequately accounted for neither by elasticity theory nor by empirical interatomic potentials.

[en] We demonstrate that biological molecules such as Watson–Crick DNA base pairs can behave as biological Aviram–Ratner electrical rectifiers because of the spatial separation and weak hydrogen bonding between the nucleobases. We have performed a parallel computational implementation of the ab initio non-equilibrium Green’s function (NEGF) theory to determine the electrical response of graphene—base-pair—graphene junctions. The results show an asymmetric (rectifying) current–voltage response for the cytosine–guanine base pair adsorbed on a graphene nanogap. In sharp contrast we find a symmetric response for the thymine–adenine case. We propose applying the asymmetry of the current–voltage response as a sensing criterion to the technological challenge of rapid DNA sequencing via graphene nanogaps. (paper)

[en] Using model calculations, we demonstrate a very high level of control of the spin-transfer torque (STT) by electric field in multiferroic tunnel junctions with composite dielectric/ferroelectric barriers. We find that, for particular device parameters, toggling the polarization direction can switch the voltage-induced part of STT between a finite value and a value close to zero, i.e. quench and release the torque. Additionally, we demonstrate that under certain conditions the zero-voltage STT, i.e. the interlayer exchange coupling, can switch sign with polarization reversal, which is equivalent to reversing the magnetic ground state of the tunnel junction. This bias- and polarization-tunability of the STT could be exploited to engineer novel functionalities such as softening/hardening of the bit or increasing the signal-to-noise ratio in magnetic sensors, which can have important implications for magnetic random access memories or for combined memory and logic devices. (paper)

[en] We have employed the semidiscrete variational generalized Peierls-Nabarro model to study the dislocation properties of aluminum. The generalized-stacking-fault (GSF) energy surface entering the model is calculated by using first-principles density functional theory (DFT) and the embedded-atom method (EAM). Various core properties, including the core width, dissociation behavior, energetics, and Peierls stress for different dislocations have been investigated. The correlation between the core energetics and the Peierls stress with the dislocation character has been explored. Our results reveal a simple relationship between the Peierls stress and the ratio between the core width and the atomic spacing. The dependence of the core properties on the two methods for calculating the GSF energy (DFT vs EAM) has been examined. Although the EAM gives the general trend for various dislocation properties, it fails to predict the correct finer core structure, which in turn can affect the Peierls stress significantly (about one order of magnitude). (c) 2000 The American Physical Society