| 21. |
- Ahlberg, Martina, et al.
(författare)
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Reversed interface effects in amorphous FeZr/AlZr multilayers
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 90:18, s. 184403-
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Tidskriftsartikel (refereegranskat)abstract
- We report an anomalous enhancement of the critical temperature (T-c) when the thickness (d) of the magnetic layer is decreased from 60 to 20 angstrom in amorphous FeZr/AlZr multilayers. Further reduction of the thickness causes a decrease of T-c, as expected by finite-size scaling, while the magnetic moment decreases monotonically for all values of d. The increase of the critical temperature is attributed to a reversed interface effect where local changes in the nearest-neighbor distance and coordination number gives a higher effective magnetic coupling at the interfaces compared to the interior of the layer. We have successfully described the results within a model where such interface effects are combined with finite-size scaling.
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| 22. |
- Ahlberg, Martina, et al.
(författare)
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Two-dimensional XY-like amorphous Co68Fe24Zr8/Al70Zr30 multilayers
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 83:22, s. 224404-
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Tidskriftsartikel (refereegranskat)abstract
- We present an experimental realization of a magnetic two-dimensional XY system using amorphous materials. The classification of the dimensionality is based on the critical behavior of amorphous Co68Fe24Zr8(d)/Al70O30 (20 angstrom) multilayers, where d = 11 - 16 angstrom. Analysis of the remanent magnetization, the magnetic isotherms, the initial susceptibility, and the magnetic correlation length shows that the magnetic phase transition can be described by the 2D XY model. The samples are not paramagnetic above the critical temperature but are characterized by local magnetic order manifested in the field and temperature dependence of the magnetization. Furthermore, an average spin-spin interaction length of 8.1 angstrom was estimated using the thickness dependence of the Curie temperature.
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| 23. |
- Ahmed, T., et al.
(författare)
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G W quasiparticle calculations with spin-orbit coupling for the light actinides
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 89:3, s. 035104-
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Tidskriftsartikel (refereegranskat)abstract
- We report on the importance of GW self-energy corrections for the electronic structure of light actinides in the weak-to-intermediate coupling regime. Our study is based on calculations of the band structure and total density of states of Np, U, and Pu using a one-shot GW approximation that includes spin-orbit coupling within a full potential LAPW framework. We also present RPA screened effective Coulomb interactions for the f-electron orbitals for different lattice constants, and show that there is an increased contribution from electron-electron correlation in these systems for expanded lattices. We find a significant amount of electronic correlation in these highly localized electronic systems.
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| 24. |
- Ahola-Tuomi, M., et al.
(författare)
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Properties of self-assembled Bi nanolines on InAs(100) studied by core-level and valence-band photoemission, and first-principles calculations
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 83:24, s. 245401-
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Tidskriftsartikel (refereegranskat)abstract
- We have studied self-assembled bismuth (Bi) nanolines on the Bi-terminated InAs(100) surface by core-level and valence-band photoelectron spectroscopy, and ab initio first-principles calculations. A structural model for this intriguing surface is suggested based on the comparison of the measured and calculated core-level shifts. Also, the atomic origins for the core-level shifts are proposed based on the calculations. A clear peak related to this surface was observed in the valence band 0.34 eV below the Fermi level, which can be used as a "fingerprint" of a well-ordered Bi/InAs(100) nanoline surface.
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| 25. |
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| 26. |
- Aichhorn, Markus, et al.
(författare)
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Importance of electronic correlations for structural and magnetic properties of the iron pnictide superconductor LaFeAsO
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 84:5, s. 054529-
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Tidskriftsartikel (refereegranskat)abstract
- We present calculations of structural and magnetic properties of the iron-pnictide superconductor LaFeAsO including electron-electron correlations. For this purpose we apply a fully charge self-consistent combination of density-functional theory with the dynamical mean-field theory, allowing for the calculation of total energies. We find that the inclusion of correlation effects gives a good agreement of the arsenic z position with experimental data even in the paramagnetic (high-temperature) phase. Going to low temperatures, we study the formation of the ordered moment in the striped spin-density-wave phase, yielding an ordered moment of about 0.60 mu(B), again in good agreement with experiments. This shows that the inclusion of correlation effects improves both structural and magnetic properties of LaFeAsO at the same time.
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| 27. |
- Aikebaier, Faluke, et al.
(författare)
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Effects of short-range electron-electron interactions in doped graphene
- 2015
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 92:15
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Tidskriftsartikel (refereegranskat)abstract
- We study theoretically the effects of short-range electron-electron interactions on the electronic structure of graphene, in the presence of substitutional impurities. Our computational approach is based on the π orbital tight-binding model for graphene, with the electron-electron interactions treated self-consistently at the level of the mean-field Hubbard model. The finite impurity concentration is modeled using the supercell approach. We compare explicitly noninteracting and interacting cases with varying interaction strength and impurity potential strength. We focus in particular on the interaction-induced modifications in the local density of states around the impurity, which is a quantity that can be directly probed by scanning tunneling spectroscopy of doped graphene. We find that the resonant character of the impurity states near the Fermi level is enhanced by the interactions. Furthermore, the size of the energy gap, which opens up at high-symmetry points of the Brillouin zone of the supercell upon doping, is significantly affected by the interactions. The details of this effect depend subtly on the supercell geometry. We use a perturbative model to explain these features and find quantitative agreement with numerical results.
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| 28. |
- Airiskallio, E., et al.
(författare)
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Third element effect in the surface zone of Fe-Cr-Al alloys
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:3
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Tidskriftsartikel (refereegranskat)abstract
- The third element effect to improve the high temperature corrosion resistance of the low-Al Fe-Cr-Al alloys is suggested to involve a mechanism that boosts the recovering of the Al concentration to the required level in the Al-depleted zone beneath the oxide layer. We propose that the key factor in this mechanism is the coexistent Cr depletion that helps to maintain a sufficient Al content in the depleted zone. Several previous experiments related to our study support that conditions for such a mechanism to be functional prevail in real oxidation processes of Fe-Cr-Al alloys.
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| 29. |
- Airiskallio, E., et al.
(författare)
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Tuning the surface chemistry of Fe-Cr by V doping
- 2009
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 80:15
-
Tidskriftsartikel (refereegranskat)abstract
- The reversal of the magnitudes of the bulk and surface chemical-potential differences induces the outburst of Cr on the otherwise pure Fe surface of Fe-Cr alloys. This threshold value for the Cr content is about 10 at. %. It is found that vanadium addition to Fe-Cr shifts the Cr threshold to a substantially lower value suggesting V having a positive effect on the corrosion resistance of low Cr steels. The obtained shift in the Cr threshold is shown to be connected to the change in volume of the alloy.
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| 30. |
- Al-Zoubi, Noura, et al.
(författare)
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Completeness of the exact muffin-tin orbitals : application to hydrogenated alloys
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:4
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the basis set convergence of the exact muffin-tin orbitals by monitoring the equation of state for Al, Cu, and Rh calculated in the conventional face-centered-cubic lattice (str-I) and in a face-centered-cubic lattice with one atomic and three empty sites per primitive cell (str-II). We demonstrate that three (spd) muffin-tin orbitals are sufficient to describe Al in both structures, but for str-II Cu and Rh at least five (spdfg) orbitals are needed to get converged equilibrium Wigner-Seitz radius (within <= 0.8%) and bulk modulus (<= 3.3%). We ascribe this slow convergence to the nearly spherical densities localized around the Cu and Rh atoms, which create strongly asymmetric charge distributions within the nearest cells around the empty sites. The potential sphere radius dependence of the theoretical results for structure str-II is discussed. It is shown that a properly optimized overlapping muffin-tin potential in combination with the spdfg basis yields acceptable errors in the equilibrium bulk properties. The basis set convergence is also shown on hydrogenated Sc and Sc-based alloys.
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