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The electronic structure and magnetism of individual Dy atom adsorbed on the graphene/Ir(1 1 1) surface is investigated using the combination of the density functional theory with the Hubbard-I approximation to the Anderson impurity model (DFT + HIA). The divalent Dy 2 + adatom is found, with the magnetic moment of 9.4–9.6 μ B , depending on the placement of the graphene on the Ir(1 1 1) surface, in an external magnetic field. The spin and orbital magnetic moments are evaluated, and compared with the X-ray magnetic circular dichroism (XMCD) data. The positive magnetic anisotropy energy determines the out-of-plane orientation of the Dy adatom magnetic moment. Without an external magnetic field, the ground state is a doublet | J = 8 , J z = ± 7.9 〉 , symmetry protected from quantum tunnelling of the magnetization. Calculations show that insertion of the graphene layer promotes reduction of the hybridization between Dy- 4 f -states and the Ir(1 1 1) substrate, and leads to increase of the magnetic moment relaxation time for the Dy adatom.

A new neptunium intermetallic compound, NpPt 2 In 7 , has been synthesized in polycrystalline form and characterized by several macroscopic techniques. A Rietveld analysis of its powder X-ray diffraction pattern shows that NpPt 2 In 7 crystallizes in a tetragonal lattice with I 4/ mmm symmetry and lattice parameters a = 4.58471 ( 3 ) A, c = 21.5065 ( 3 ) A. Magnetic susceptibility, electrical resistivity, Hall effect, and heat capacity measurements indicate a metallic character and the occurrence of antiferromagnetic order below a Neel temperature T N = 23 K. The transition is exceptionally robust and T N decreases by 0.2 K under a magnetic field of 9 T. A modified Curie-Weiss fit of the high-temperature magnetic susceptibility curve χ ( T ) gives an effective magnetic moment μ e f f = 2.54 μ B close to the value expected for trivalent Np. Low temperature heat capacity measurements give a reduced Sommerfeld linear coefficient close to 25 mJ mol −1 K −2 and a Debye Temperature Θ D = 181 K. First principles, correlated-band electronic structure calculations suggest that the neptunium magnetic moment in NpPt 2 In 7 is localized and that a quasi-two-dimensional antiferromagnetic structure could result from the competition of very weak interlayer interactions leading to very anisotropic properties.

The electronic and magnetic character, and the magnetic anisotropy in practically important magnetic materials containing the rare earth elements are investigated making use of the correlated band theory implemented as a combination of the relativistic density functional theory with the Anderson impurity model (DFT+U+HIA). First, we demonstrate that DFT+U+HIA provides a good description of the electronic structure, spin and orbital magnetic moments, and the magnetic anisotropy for SmCo5 magnet with 4f5-like Sm3+ shell. Further, the method is applied to theoretical investigation of Dy-doped Bi2Te3 topological insulator. For both ferro- and anti-ferromagnetic Dy-planes in Bi2Te3 we found the in-gap flat f-bands located at the top of the valence band of Bi2Te3. The positive uniaxial MAE is predicted for (DyxBi1−x)2Te3 with x = 0.33. The experimental resonant photoemission spectra are well reproduced by the calculations. These studies can be important to explore the potential use of rare-earth doped topological insulators in the low-power spintronic devises.

Electronic structure calculations combining the local density approximation with an exact diagonalization of the Anderson impurity model show intermediate 5f5–5f6-valence ground state and delocalization of the 5f5 multiplet of the Pu atom 5f-shell in PuCoGa5, and δ-Pu. The 5f-local magnetic moment is compensated by a moment formed in the surrounding cloud of conduction electrons. For PuCoGa5 and δ-Pu the compensation is complete and the Anderson impurity ground state is a singlet. This can be important for analyses of the superconducting pairing mechanism in PuCoGa5. It is likely that in PuCoGa5 unconventional d-wave superconductivity is mediated by the 5f-states valence fluctuations, rather than antiferromagnetic fluctuations.

The magnetic phase transitions for Gd(0 0 0 1) grown on W(1 1 0) - a bulk transition at 293 K and a surface transition about 85 K above this - are found to influence the energy separation of the Gd 5s and 4s core-photoelectron doublets. The 5s doublet separation ¿E5s changes over a range of temperatures spanning these transitions, and decreases by a maximum of 60 meV in this region, but then recovers its original value; the 4s doublet shows a smaller change in the reverse direction, which does not recover at high temperature. Some of these effects are semi-quantitatively understood from free-atom multiplet theory and from theoretical calculations based on all-electron LDA+U calculations including 4f electron correlation effects. However, the high-temperature behavior of the data also suggest a dynamical nature to these effects via spin-dependent electron screening that is influenced by magnetic fluctuations. Several avenues for studying such effects in a time-resolved manner in future experiments are discussed., Support was provided by the Director, Office of Energy Research, Mat. Sci. Div., of the U.S. Dept. of Energy, under Contracts No. DE-AC03-76SF00098 and DE-AC02-05CH11231, and the DGICyT (Grant No. PB94-0022-C02-02) MEC, Spain. Work at UC Davis (W.E.P.) was supported in part by DOE grant No. DE-FG03-03NA00071.

In the conventional Ohmic regime, magnetoresistance effects comprise the ordinary responses to the external magnetic field and extraordinary responses to the internal magnetization. Here we study magnetoresistance effects in the Coulomb blockade regime using a ferromagnetic (Ga, Mn)As single electron transistor. We report measurements of the magneto-Coulomb blockade effect due to the direct coupling of high external magnetic fields and the Coulomb blockade anisotropic magnetoresistance associated with magnetization rotations in the ferromagnet. The latter, extraordinary magnetoresistance effect is characterized by low-field hysteretic magnetoresistance which can exceed three orders of magnitude. The sign and size of this magnetoresistance signal is controlled by the gate voltage, and the data are interpreted in terms of anisotropic electrochemical shifts induced by magnetization reorientations. Non-volatile transistor-like applications of the Coulomb blockade anisotropic magnetoresistance are briefly discussed.

We observe low-field hysteretic magnetoresistance (MR) in a (Ga,Mn)As single electron transistor which can exceed three orders of magnitude. The sign and size of the MR signal is controlled by the gate voltage. Experimental data are interpreted in terms of electrochemical shifts associated with magnetization rotations. This Coulomb blockade anisotropic MR is distinct from previously observed anisotropic MR effects as it occurs when the anisotropy in a band structure derived parameter is comparable to an independent scale, the single electron charging energy. Effective kinetic-exchange model calculations in (Ga,Mn)As show chemical potential anisotropies consistent with experiment and ab initio calculations in transition-metal systems suggest that this generic effect persists to high temperatures in metal ferromagnets with strong spin–orbit coupling. In addition we observe a significant gate voltage dependence of the magnetic switching field which we attribute to carrier density variations in the electric field exposed GaMnAs regions causing a substantial change in the magneto-crystalline anisotropy profile.

The current theoretical understanding of the electronic structures of the CeMIn 5 compounds (with M=Co, Rh, and Ir) and PuCoGa 5 and PuRhGa 5 is reviewed. Both the Ce-115 and Pu-115 compounds have in common that their f-electrons appear to be poised on the edge of a localization–delocalization boundary. We consider here the implications of this characteristic on the emergent electronic structure, addressing, in particular, the computed Fermi surfaces. In order to capture the electronic structures to the best as possible, we employ three different density-functional theory based computational approaches, viz. the local-spin density approximation (LSDA) for delocalized f-states, the open-core approach for localized f's, and the LSDA+ U approach for moderately localized f's. The Fermi surfaces of CeCoIn 5 and CeIrIn 5 are rather well described assuming delocalized 4f electrons. Conversely, the better description is obtained for CeRhIn 5 assuming a localized 4f state. For the Pu-115 compounds, LSDA calculations predict a rather two-dimensional Fermi surface. However, the Fermi surface of PuCoGa 5 computed with the around-mean field LSDA+ U scheme is also quite two-dimensional and, moreover, similar to the LSDA Fermi surface. Taking other available experimental data on PuCoGa 5 into account, it appears that the electronic structure of PuCoGa 5 is best described by the AMF-LSDA+ U approach with a Coulomb U of about 3 eV.

The local-density approximation combined with the dynamical mean-field theory (LDA+DMFT) is applied to the paramagnetic phase of light actinide dioxides: UO2, NpO2, and PuO2. The calculated band gaps and the valence-band electronic structure are in a very good agreement with the optical absorption experiments as well as with the photoemission spectra. The hybridization of the actinide 5f shell with the 2p states of oxygen is found to be relatively large, it increases the filling of the 5f orbitals from the nominal ionic configurations with two, three, and four electrons to nearly half-integer values 2.5, 3.4 and 4.4. The large hybridization leaves an imprint also on the core-level photoemission spectra in the form of satellite peaks. It is demonstrated that these satellites are accurately reproduced by the LDA+DMFT calculations., REVTeX 4-1, 10 pages, 6 figures

First principles calculations are used to investigate a monatomic Co chain at the Pt(111) surface step edge. We optimize the system geometry minimizing the atomic forces and evaluate the magnetocrystalline anisotropy energy (MAE). The easy magnetization axis is found to align perpendicular to the Co-wire at an angle of ≈ 50° (A-step) and ≈ 30° (B-step) towards the Pt step and the calculated MAE of 2.8meV (A-step) and 4.45 meV (B-step) are in good agreement with experiment. Our calculations show that the structural relaxation improves the quantitative description of the MAE.

Analysis of available photoelectron spectra from Pu compounds indicates the presence of the 5f5 multiplet, which dominates the energy scale close to the Fermi level. As shown by the LDA+U+Hubbard I calculations, its intensity scales with the admixture of the 5f6 manifold in the 5f5 ground state, which can lead to an average occupancy substantially exceeding 5.0. This admixture also leads to the suppression of magnetic order and occurrence of heavy fermion behaviour.

Weakly paramagnetic character of δ-Pu is preserved when Pu is doped by Am, which expands the crystal lattice. Specific-heat data show that the γ -coefficient does not increase. Such behaviour can be understood on the basis of LSDA+U calculations, which yield invariably non-magnetic Pu state due to the proximity to the 5f 6 state. We suggest that a general condition for Pu magnetism is some degree of a hybridization with states of other elements in alloys and compounds, which allows for the reduction of the 5f count.

We have performed full-potential linearized augmented plane wave calculations of the Gd(0001) surface using the local density approximation (LDA) together with the Hubbard U (LDA+U) total energy functional. The use of LDA+U instead of LDA total energy calculations leads to a ferromagnetic ground state for both bulk Gd and the Gd surface, in agreement with experimental observation. The calculated downward shift of 4f eigenvalues for the Gd surface is in agreement with experimentally observed binding energies. Surface strain relaxation leads to a 90% enhancement of the interlayer surface-to-bulk effective exchange coupling. Application of a Landau–Ginzburg-type theory yields a 30% enhancement of the Curie temperature at the surface, in very good agreement with the experiment.

The magnetoelastic coupling and magnetic anisotropy energy (MAE) of (i) an uncovered and (ii) a Cu-capped Co overlayer on Cu(001) are determined employing a self-consistent relativistic spin-polarized version of the total-energy full-potential linearized augmented plane-wave (FLAPW) method and the magnetic torque method. Layer-resolved contributions to the magnetoelastic coupling and MAE are obtained. We find surface magnetoelastic coupling coefficients to be positive for the Co layer and negative for the Cu substrate and cap layers. A substantial difference of magnetoelastic coupling coefficients for thin films as opposed to bulk is demonstrated, which causes a negative magnetostriction coefficient (λ001) for uncovered Co overlayer and a positive λ001 for the Cu-capped Co overlayer on Cu(001).

Valence-band photoelectron spectra of Pu2C3 and PuC0.85 reveal the same type of 5f features below the Fermi level as observed for majority of other Pu systems. They appear at the same energies (0–0.1, 0.5, and 0.85 eV) and their intensity is higher for Pu2C3 than for PuC0.85. They can be attributed to the 5f5 final-state multiplet originating in the 5f6 component of the ground state. The higher 5f occupancy (5.48) calculated in Pu2C3, explains its non-magnetic character.

Selected electronic properties of Pu, Am, Cm and Bk are calculated with the aid of charge self-consistent LDA + Hubbard I method. Presented all-electron calculations are performed in the full-potential LAPW basis and incorporate spin-orbit interaction. The results are found to be in good agreement with experimental valence photoelectron spectra as well as with core XAS/EELS spectra of heavy actinides.

This contribution focuses on the structural and physical properties of U-based Laves phases. It starts with the structural description of the different type of Laves phases, followed by a brief description of the factors that affect their stability. The majority of the uranium Laves phases show a weakly paramagnetic behaviour. The reason is the compact structure of the phases that leads to small a U-U spacing as well as very high coordination numbers, regarding both the uranium and the ligands sublattices, which brings a strong hybridization with non-f states. However, there are some exceptions of uranium Laves phases that do order magnetically (UFe2, UNi2 and the recently discovered U2Fe3Ge compound). These exceptions are discussed in more detail in the present manuscript.

Occurrence of magnetic order on the basis of plutonium can be captured by LDA+U calculations. Systematic investigation of diverse Pu compounds reveals that the 5f occupancy plays a key role. If the 5f states are populated by more than approximately 5.3 electrons, the Pu magnetism vanishes. For comparison with valence-band photoemission spectra, the Hubbard I method was used. It shows consistently higher 5f5 final-state multiplet originating from the 5f6 admixture in the ground state for those compounds which are nonmagnetic. The 5f occupancy can reach 5.6–5.7 for Pu monochalcogenides.

The magnetic anisotropy energy for a single Co atom on CuN/Cu(001) surface is investigated making use of the first-principles relativistic local spin density approximation (LSDA) calculations and the torque method. A single-ion character of the magnetic anisotropy is revealed, which originates mainly from the local magnetic moment of the Co atom. The effect of the orbital polarization beyond that given by the LSDA is studied making use of the different flavors of the LDA+U method. It is shown that the LDA+U induced orbital polarization affects the orbital component of the magnetic moment for different directions of the Co-atom magnetization and can modify substantially the magnetic anisotropy energy. Comparison with the available experimental data is discussed.

Valence-band photoelectron spectra of Pu2C3 and PuC0.85 reveal the same type of 5f features below the Fermi level as observed for the majority of other Pu systems. They appear at the same energies (0–0.1, 0.5, and 0.85 eV) and their intensity is higher for Pu2C3 than for PuC0.85. We deduce that they can be attributed to the 5f5 final-state multiplet originating in the 5f6 component of the ground state. The higher 5f occupancy (5.48), calculated in Pu2C3, explains its non-magnetic character.

We propose a straightforward and efficient procedure to perform dynamical mean-field (DMFT) calculations on the top of the static mean-field LDA+U approximation. Starting from self-consistent LDA+U ground state we included multiplet transitions using the Hubbard-I approximation, which yields a very good agreement with experimental photoelectron spectra of $\delta$-Pu, Am, and their selected compounds., Comment: submitted to Europhysics Letters