The Fermi Surface Effect on Magnetic Interlayer Coupling

The oscillating magnetic interlayer coupling of Fe over spacer layers consisting of Cu$_{x}$Pd$_{1-x}$ alloys is investigated by first principles density functional theory. The amplitude, period and phase of the coupling, as well as the disorder-induced decay, are analyzed in detail and the consistency to the Ruderman-Kittel-Kasuya-Yoshida (RKKY) theory is discussed. For the first time an effect of the Fermi surface nesting strength on the amplitude is established from first principles calculations. An unexpected variation of the phase and disorder-induced decay is obtained and the results are discussed in terms of asymptotics

Ballistic Spin Injection from Fe into ZnSe and GaAs with a (001), (111), and (110) orientation

We present first-principles calculations of ballistic spin injection in Fe/GaAs and Fe/ZnSe junctions with orientation (001), (111), and (110). We find that the symmetry mismatch of the Fe minority-spin states with the semiconductor conduction states can lead to extremely high spin polarization of the current through the (001) interface for hot and thermal injection processes. Such a symmetry mismatch does not exist for the (111) and (110) interfaces, where smaller spin injection efficiencies are found. The presence of interface states is found to lower the current spin polarization, both with and without a Schottky barrier. Finally, a higher bias can also affect the spin injection efficiency.Comment: 12 pages, 18 figure

Parasitism of the root-lesion nematode Pratylenchus thornei on chickpea

Pratylenchus thornei-chickpea interactions were investigated under controlled and fluctuating environmental conditions in the growth chamber, greenhouse and shadehouse. Under controlled conditions. P. thornei infected chickpea hnes 12071/10054 and P2245 and cultivars Andoum 1, JG62 and UC 27. Line P 2245 and cv. JG 62 were the most susceptible genotypes on the basis of root damage and nematode reproduction, but nematode infection did not significantly reduce root and shoot weights. Cultivars Andoum 1 and UC27 and line 12071/10054 showed the least root damage and nematode reproduction. Inoculation of cv. Andoum 1 with 2500, 5000 or lOOOO nematodes per plant in pots did not affect shoot weight, regardless ofthe conditions of water stress ofthe plants. However, root weight was significantly reduced by nematode infection in plants grown under water stress and fluctuating temperature conditions in the greenhouse, but was not affected by any other treatment. The nematode reproduction index was not affected by soil water content under shadehouse conditions, but was greater on plants watered to soil water-holding capacity than in water-stressed plants under greenhouse conditions. For both environments, the nematode reproduction index decreased when inoculum density was greater than 5000 nematodes per plant.This research was supported by grant AGF92- 0910-CO2-01 from Comision Interministerial de Ciencia y Technologia (CICYT), We thank H, M, Halila, INRA, Tunisia for providing us with seeds of cultivar Andoum 1, and F, Orgaz, Instituto de Agricultura Sostenible, CSIC, Spain for measuring water potential.Peer reviewe

Ising cubes with enhanced surface couplings

Using Monte Carlo techniques, Ising cubes with ferromagnetic nearest-neighbor interactions and enhanced couplings between surface spins are studied. In particular, at the surface transition, the corner magnetization shows non-universal, coupling-dependent critical behavior in the thermodynamic limit. Results on the critical exponent of the corner magnetization are compared to previous findings on two-dimensional Ising models with three intersecting defect lines.Comment: 4 pages, 2 figures included, submitted to Phys. Rev.

Surface Half-Metallicity of CrAs in the Zinc-Blende Structure

The development of new techniques such as the molecular beam epitaxy have enabled the growth of thin films of materials presenting novel properties. Recently it was made possible to grow a CrAs thin-film in the zinc-blende structure. In this contribution, the full-potential screened KKR method is used to study the electronic and magnetic properties of bulk CrAs in this novel phase as well as the Cr and As terminated (001) surfaces. Bulk CrAs is found to be half-ferromagnetic for all three GaAs, AlAs and InAs experimental lattice constants with a total spin magnetic moment of 3 $\mu_B$. The Cr-terminated surface retains the half-ferromagnetic character of the bulk, while in the case of the As-termination the surface states destroy the gap in the minority-spin band.Comment: 4 pages, 2 figures, new text, new titl

Fully relativistic calculation of magnetic properties of Fe, Co and Ni adclusters on Ag(100)

We present first principles calculations of the magnetic moments and magnetic anisotropy energies of small Fe, Co and Ni clusters on top of a Ag(100) surface as well as the exchange-coupling energy between two single adatoms of Fe or Co on Ag(100). The calculations are performed fully relativistically using the embedding technique within the Korringa-Kohn-Rostoker method. The magnetic anisotropy and the exchange-coupling energies are calculated by means of the force theorem. In the case of adatoms and dimers of iron and cobalt we obtain enhanced spin moments and, especially, unusually large orbital moments, while for nickel our calculations predict a complete absence of magnetism. For larger clusters, the magnitudes of the local moments of the atoms in the center of the cluster are very close to those calculated for the corresponding monolayers. Similar to the orbital moments, the contributions of the individual atoms to the magnetic anisotropy energy strongly depend on the position, hence, on the local environment of a particular atom within a given cluster. We find strong ferromagnetic coupling between two neighboring Fe or Co atoms and a rapid, oscillatory decay of the exchange-coupling energy with increasing distance between these two adatoms.Comment: 8 pages, ReVTeX + 4 figures (Encapsulated Postscript), submitted to PR

Ab-initio calculation of Kerr spectra for semi-infinite systems including multiple reflections and optical interferences

Based on Luttinger's formulation the complex optical conductivity tensor is calculated within the framework of the spin-polarized relativistic screened Korringa-Kohn-Rostoker method for layered systems by means of a contour integration technique. For polar geometry and normal incidence ab-initio Kerr spectra of multilayer systems are then obtained by including via a 2x2 matrix technique all multiple reflections between layers and optical interferences in the layers. Applications to Co|Pt5 and Pt3|Co|Pt5 on the top of a semi-infinite fcc-Pt(111) bulk substrate show good qualitative agreement with the experimental spectra, but differ from those obtained by applying the commonly used two-media approach.Comment: 32 pages (LaTeX), 5 figures (Encapsulated PostScript), submitted to Phys. Rev.

Exercise-induced modulation of cardiac lipid content in healthy lean young men

Cardiac lipid accumulation is associated with decreased cardiac function and energy status (PCr/ATP). It has been suggested that elevated plasma fatty acid (FA) concentrations are responsible for the cardiac lipid accumulation. Therefore, the aim of the present study was to investigate if elevating plasma FA concentrations by exercise results in an increased cardiac lipid content, and if this influences cardiac function and energy status. Eleven male subjects (age 25.4 ± 1.1 years, BMI 23.6 ± 0.8 kg/m2) performed a 2-h cycling protocol, once while staying fasted and once while ingesting glucose, to create a state of high versus low plasma FA concentrations, respectively. Cardiac lipid content was measured by proton magnetic resonance spectroscopy (1H-MRS) at baseline, directly after exercise and again 4 h post-exercise, together with systolic function (by multi-slice cine-MRI) and cardiac energy status (by 31P-MRS). Plasma FA concentrations were increased threefold during exercise and ninefold during recovery in the fasted state compared with the glucose-fed state (p < 0.01). Cardiac lipid content was elevated at the end of the fasted test day (from 0.26 ± 0.04 to 0.44 ± 0.04%, p = 0.003), while it did not change with glucose supplementation (from 0.32 ± 0.03 to 0.26 ± 0.05%, p = 0.272). Furthermore, PCr/ATP was decreased by 32% in the high plasma FA state compared with the low FA state (n = 6, p = 0.014). However, in the high FA state, the ejection fraction 4 h post-exercise was higher compared with the low FA state (63 ± 2 vs. 59 ± 2%, p = 0.018). Elevated plasma FA concentrations, induced by exercise in the fasted state, lead to increased cardiac lipid content, but do not acutely hamper systolic function. Although the lower cardiac energy status is in line with a lipotoxic action of cardiac lipid content, a causal relationship cannot be proven

Origin and Properties of the Gap in the Half-Ferromagnetic Heusler Alloys

We study the origin of the gap and the role of chemical composition in the half-ferromagnetic Heusler alloys using the full-potential screened KKR method. In the paramagnetic phase the C1_b compounds, like NiMnSb, present a gap. Systems with 18 valence electrons, Z_t, per unit cell, like CoTiSb, are semiconductors, but when Z_t > 18 antibonding states are also populated, thus the paramagnetic phase becomes unstable and the half-ferromagnetic one is stabilized. The minority occupied bands accommodate a total of nine electrons and the total magnetic moment per unit cell in mu_B is just the difference between Z_t and $2 \times 9$. While the substitution of the transition metal atoms may preserve the half-ferromagnetic character, substituting the $sp$ atom results in a practically rigid shift of the bands and the loss of half-metallicity. Finally we show that expanding or contracting the lattice parameter by 2% preserves the minority-spin gap.Comment: 11 pages, 7 figures New figures, revised tex