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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 report computational investigations of the electronic structures of the superconducting Pu-compounds PuCoGa5 as well as of the non-superconducting compounds PuFeGa5 and PuNiGa5. To capture the localization behavior of the Pu 5f electrons, we apply two computational approaches, which are both rooted in the density-functional theory: the local spin-density approximation (LSDA) and the around mean field (AMF) LSDA + U approach. The latter is applicable to moderately localized 5f electrons while the former is applicable to delocalized 5f electrons. Our LSDA calculations show that the Fermi surfaces of the three Pu-115 compounds are sensitive to the amount of band filling, i.e., the number of electrons of the 3d element. Precisely at the electron filling corresponding to PuCoGa5 the Fermi surface has a particularly two-dimensional shape. AMF–LSDA + U calculations (with a Coulomb U of about 3 eV and exchange J of 0.6 eV) lead to a non-magnetic ground state for PuCoGa5, in which the 5f states are shifted to a higher binding energy, in better agreement with photoemission data. The Fermi surface of PuCoGa5 computed with the AMF–LSDA + U approach is nonetheless rather two-dimensional and similar to the LSDA Fermi surface. The AMF–LSDA + U approach with a Coulomb U of ≈ 3 eV would thus predict an electronic structure for PuCoGa5 in accord with several experimental data.

The possibility of the 5f count variations and its impact on magnetic properties are discussed on the background of known data on diluted alloys, intermetallic compounds and monopnictides and monochalcogenides. 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. It is also shown that the ground-state density of states should not be directly compared with photoelectron spectra, because the spectral density obtained from Hubbard-I calculations is in the narrow band regime of Pu dramatically different than the underlying density of states. We suggest that a general condition for Pu magnetism is some degree of hybridization with states of other elements in alloys and compounds, which allows for the reduction of the 5f count.

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.

We report a first-principles investigation of the anomalous magnetic anisotropy of quasi-one-dimensional ferromagnetic Fe and Co chains decorating the Pt(1 1 1) step edge. Our calculations for both Fe and Co wires show that the easy magnetization is always confined in the plane perpendicular to the wire. The symmetry breaking at the step leads to an easy magnetization axis of the Co wire at an odd angle of ∼ 20 ∘ towards the Pt step, in agreement with the experiment. This canting becomes more pronounced for the Fe wire, for which we obtain an easy axis at 30 ∘ towards the Pt step. Also, the Fe and Co spin and orbital moments become noncollinear, even in the case of a collinear ferromagnetic spin arrangement.

The effects of electron correlation on the electronic structure and spin and orbital magnetic properties of the f.c.c. Ce were investigated using the relativistic (with spin–orbit coupling included) full-potential linearized augmented plane wave implementation of correlated band theory (‘LDA+U’). Multiple energy minima of the LDA+U energy functional are obtained for γ-Ce. The lowest energy solution leads to a fully spin polarized 4f state and the lattice constant of γ-Ce. The higher energy local minima (additional self-consistent solutions) are shown to be strongly indicative of low-energy excitations.

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.

Thin layers of PuCoGax (x = 4 to 18) have been prepared by dc sputtering from a PuCoGa5 single crystal target, and investigated in situ by X-ray and ultraviolet photoelectron spectroscopy. We could achieve broad composition variability (monitored by the Pu-4f, Co-2p and Ga-2p core-level spectra). The results are compared to the valence band spectra reported previously for PuCoGa5. Our experiments reveal that some Ga excess (PuCoGa≈7) was likely for those original data. We demonstrate that there is a tendency to the segregation of Ga at the surface, which has an important effect on the valence band spectra.

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.

Recent developments in the first-principles determination of magneto-crystalline anisotropy (MCA) and magnetostrictive coefficients in transition metal systems are reviewed. With the aid of our newly developed state tracking and torque approaches, high numerical stability can be achieved for the MCA energy, the essential ingredient of the magnetostriction. Very smooth monotonic behavior of the MCA energy with respect to the lattice strain was found for most of the systems studied. The calculated magnetostrictive coefficients are positive for BCC Fe and FCC Co but negative for FCC Ni — a result which agrees well with experiments. This can be explained simply through the strain induced d-band broadening and shifting. For Co/Cu(0 0 1), Co/Pd(0 0 1) and Co/Pd(1 1 1) thin films, the magnetostrictive coefficients are found to be very sensitive to the change of substrates and even orientation.

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.

We investigate the effect of an H-adlayer on the magnetic anisotropy energy (MAE) of Ni / Cu (0 0 1) making use of the total energy full-potential linearized augmented plane wave (FP-LAPW) method including spin–orbit coupling, and taking into account crystal structure relaxation effects. We find strong influence of H-adlayer on the surface MAE, providing the reduction of spin-reorientation transition critical thickness, in accordance with the recent experiments.

The magnetoelastic coupling and magnetic anisotropy energy (MAE) of a Co overlayer on Cu(0 0 1) is studied employing a self-consistent relativistic spin-polarized version of the total energy full potential linearized augmented plane wave (FLAPW) method. We find a magnetostriction coefficient, λ 0 0 1 , which is in good agreement with a previous study based on a perturbative SOC treatment, and has a negative sign caused by a positive surface magnetoelastic anisotropy, and the substantial difference of magnetoelastic coupling coefficients for thin films, as opposed to bulk, is demonstrated.