Reorientation phase transitions in thin magnetic films: a review of the classical vector spin model within the mean field approach

The ground state and the finite temperature phase diagrams with respect to magnetic configurations are studied systematically for thin magnetic films in terms of a classical Heisenberg model including magnetic dipole-dipole interaction and uniaxial anisotropy. Simple relations are derived for the occurrence of the various phase boundaries between the different regions of the magnetic orientations. In particular, the range of the first and second order reorientation phase transitions are determined for bi- and trilayers.Comment: 23 pages, LaTeX + 7 figures (Encapsulated PostScript), submitted to Philosophical Magazine B (Feb. 28, 2001

Magnetic phase diagram of an Fe monolayer on W(110) and Ta(110) surfaces based on ab initio calculations

We present detailed investigations of the magnetic properties of an Fe monolayer on W and Ta (110) surfaces based on the ab initio screened Korringa-Kohn-Rostoker method. By calculating tensorial exchange coupling coefficients, the ground states of the systems are determined using atomistic spin dynamics simulations. Different types of ground states are found in the systems as a function of relaxation of the Fe layer. In case of W(110) substrate this is reflected in a reorientation of the easy axis from in-plane to out-of-plane. For Ta(110) a switching appears from the ferromagnetic state to a cycloidal spin spiral state, then to another spin spiral state with a larger wave vector and, for large relaxations, a rotation of the normal vector of the spin spiral is found. Classical Monte Carlo simulations indicate temperature-induced transitions between the different magnetic phases observed in the Fe/Ta(110) system. These phase transitions are analyzed both quantitatively and qualitatively by finite-temperature spin wave theory.Comment: 18 pages, 11 figure

Layer-resolved optical conductivity of Co|Pt multilayers

The complex optical conductivity tensor is calculated for the Co|Pt systems by applying a contour integration technique within the framework of the spin-polarized relativistic screened Korringa-Kohn-Rostoker method. It is shown that the optical conductivity of the Co|Pt multilayer systems is dominated by contributions arising from the Pt cap and/or substrate layers.Comment: 7 pages (LaTeX), 2 (a,b) figures (Encapsulated PostScript), J. Magn. Magn. Materials, in pres

Anisotropy of ultra-thin ferromagnetic films and the spin reorientation transition

The influence of uniaxial anisotropy and the dipole interaction on the direction of the magnetization of ultra-thin ferromagnetic films in the ground-state is studied. The ground-state energy can be expressed in terms of anisotropy constants which are calculated in detail as function of the system parameters and the film thickness. In particular non-collinear spin arrangements are taken into account. Conditions for the appearance of a spin reorientation transition are given and analytic results for the width of the canted phase and its shift in applied magnetic fields associated with this transition are derived.Comment: 6 pages, RevTeX

A dicarboxylate transporter on the peribacteroid membrane of soybean nodules

AbstractUsing preparations of peribacteroid membrane (PBM)-enclosed bacteroids from soybean root nodules, we show here that the PBM possesses a dicarboxylate transporter capable of mediating a rapid flux of dicarboxylate anions, such as malate and succinate, to the bacteroids inside the nodule. The transporter has a higher affinity for the monovalent malate anion than for the succinate anion (Km = 2 and 15 μM, respectively) although the Vmax for malate− appears to be lower than for succinate− (Vmax = 11 and 30 nmol·min−1·mg protein−1, respectively)

TransportTP: A two-phase classification approach for membrane transporter prediction and characterization

<p>Abstract</p> <p>Background</p> <p>Membrane transporters play crucial roles in living cells. Experimental characterization of transporters is costly and time-consuming. Current computational methods for transporter characterization still require extensive curation efforts, especially for eukaryotic organisms. We developed a novel genome-scale transporter prediction and characterization system called TransportTP that combined homology-based and machine learning methods in a two-phase classification approach. First, traditional homology methods were employed to predict novel transporters based on sequence similarity to known classified proteins in the Transporter Classification Database (TCDB). Second, machine learning methods were used to integrate a variety of features to refine the initial predictions. A set of rules based on transporter features was developed by machine learning using well-curated proteomes as guides.</p> <p>Results</p> <p>In a cross-validation using the yeast proteome for training and the proteomes of ten other organisms for testing, TransportTP achieved an equivalent recall and precision of 81.8%, based on TransportDB, a manually annotated transporter database. In an independent test using the Arabidopsis proteome for training and four recently sequenced plant proteomes for testing, it achieved a recall of 74.6% and a precision of 73.4%, according to our manual curation.</p> <p>Conclusions</p> <p>TransportTP is the most effective tool for eukaryotic transporter characterization up to date.</p

Recent insights into antioxidant defenses of legume root nodules

43 Pag., 2 Tabl., 2 Fig. The definitive version is available at: www3.interscience.wiley.comLegume root nodules are sites of intense biochemical activity and consequently are at high risk of damage as a result of the generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS). These molecules can potentially give rise to oxidative and nitrosative damage but, when their concentrations are tightly controlled by antioxidant enzymes and metabolites, they also play positive roles as critical components of signal transduction cascades during nodule development and stress. Thus, recent advances in our understanding of ascorbate and (homo)glutathione biosynthesis in plants have opened up the possibility of enhancing N2 fixation through an increase of their concentrations in nodules. It is now evident that antioxidant proteins other than the ascorbate-glutathione enzymes, such as some isoforms of glutathione peroxidases, thioredoxins, peroxiredoxins, and glutathione S-transferases, are also critical for nodule activity. To avoid cellular damage, nodules are endowed with several mechanisms for sequestration of Fenton-active metals (nicotianamine, phytochelatins, and metallothioneins) and for controlling ROS/RNS bioactivity (hemoglobins). The use of ‘omic’ technologies has expanded the list of known antioxidants in plants and nodules that participate in ROS/RNS/antioxidant signaling networks, although aspects of developmental variation and subcellular localization of these networks remain to be elucidated. To this end, a critical point will be to define the transcriptional and post-transcriptional regulation of antioxidant proteins.The research described here was supported by a grant from the National Science Foundation (IOS-0517688) to D.A.D., and a grant from the Spanish Ministry of Science and Innovation-FEDER (AGL2008-01298) and Government of Aragón (group A53) to M.B.Peer reviewe

Theory for transport through a single magnetic molecule: Endohedral N@C60

We consider transport through a single N@C60 molecule, weakly coupled to metallic leads. Employing a density-matrix formalism we derive rate equations for the occupation probabilities of many-particle states of the molecule. We calculate the current-voltage characteristics and the differential conductance for N@C60 in a break junction. Our results reveal Coulomb-blockade behavior as well as a fine structure of the Coulomb-blockade peaks due to the exchange coupling of the C60 spin to the spin of the encapsulated nitrogen atom.Comment: 5 pages, 4 figures, v2: version as publishe

Lattice-gas model for alkali-metal fullerides: face-centered-cubic structure

A lattice-gas model is suggested for describing the ordering phenomena in alkali-metal fullerides of face-centered-cubic structure assuming the electric charge of alkali ions residing in either octahedral or tetrahedral interstitial sites is completely screened by the first-neighbor C_60 molecules. This approximation allows us to derive an effective ion-ion interaction. The van der Waals interaction between the ion and C_60 molecule is characterized by introducing an additional energy at the tetrahedral sites. This model is investigated by using a three-sublattice mean-field approximation and a simple cluster-variation method. The analysis shows a large variety of phase diagrams when changing the site energy parameter.Comment: 10 twocolumn pages (REVTEX) including 12 PS figure