Local Spin Density Functional Formalism Research Articles

Spin-Density-Wave Order and Interlayer Magnetic Coupling in Fe/Cr Superlattices

A first-principles electronic structure calculation for Fe/Cr superlattices with layered structures is performed by means of the Korringa-Kohn-Rostoker Green function method within the framework of the local spin density functional formalism. The calculation is carried out for periodic superlattices which consist of ferromagnetic Fe layers and antiferromagnetic or spin-density-wave Cr layers, with magnetizations of two successive Fe layers being aligned parallel or antiparallel, and interlayer magnetic coupling is evaluated by the total energy difference between the parallel and antiparallel couplings. It is shown that the interlayer magnetic coupling oscillates between parallel and antiparallel with a two-monolayer period of the spacer thickness of the Cr layer but the oscillation involves a phase slip around a critical thickness of 16 monolayers, at which the magnetic order in the Cr layer changes from the antiferromagnetic one to the spin-density-wave one. Characteristics of the spin-density-wave order...

Magnetism of Fe impurities and adatoms on Pd(0 0 1) surfaces

It is well known that the giant moment associated with the substitutional Fe impurities in Pd can be understood in terms of a polarization cloud consisting of small induced moments in the Pd shells around the impurity. It is interesting to investigate if a similar phenomenon is present when a Pd surface is considered. Here we perform first-principles, self-consistent electronic structure calculations, within the local spin density functional formalism, to obtain the magnetic behavior of substitutional Fe impurities in Pd(0 0 1) and Fe adatoms on this surface. We find that in both cases the Fe site has a large local moment, close to saturation. As in the case of Fe impurities in bulk Pd, a moment is induced on the Pd neighbors, considerably enhancing the total magnetic moment of the system. Our results indicate that the failure to observe magnetic behavior using anomalous Hall effect experiments for Pd surfaces with small Fe coverages cannot be explained in terms of an antiferromagnetic coupling between the Fe impurity and its Pd neighbors, as was previously suggested.

Total Energy Calculation for Spin-Density-Wave Chromium

The total energy of the spin-density-wave state in chromium is calculated by means of the first-principles Korringa-Kohn-Rostoker Green function method within the framework of the local spin density functional formalism. The calculation for the case of the experimental lattice constant shows that the total energy per atom becomes the lowest at a wave vector close to the observed ordering wave vector of spin-density-wave chromium. The calculation with varying the lattice constant shows that the total energy of the spin-density-wave states does not become minimum against the change of the lattice constant, and it may be concluded that the theoretical ground state at the total energy minimum for chromium is a nonmagnetic state, though on the verge of a transition to a spin-density-wave state. The effect of the periodic lattice distortion due to the charge density wave, which usually accompanies the spin density wave, on the total energy is further investigated.

First-principles KKR calculation for spin-density-wave chromium

A first-principles electronic structure calculation for spin-density-wave chromium by means of the Korringa-Kohn-Rostoker method in the local spin-density functional formalism is presented. It is found that the calculation for the case of the experimental lattice constant is in good agreement with the experiments concerning the magnetism in spin-density-wave chromium.

Magnetism in Spin-Density-Wave Chromium from First-Principles Calculation

The electronic structure of the spin-density-wave state in chromium is calculated by means of the first-principles Korringa-Kohn-Rostoker Green function method within the framework of the local spin density functional formalism. Results of the calculation are found to be in good agreement with those of experiments concerning the magnetism in spin-density-wave chromium, that is, the amplitude of the fundamental wave and the ordering wave vector. The amplitudes of the harmonics of the spin density wave and concomitant charge density wave as well as the hyperfine field at a chromium nucleus are furthermore investigated.

Electronic structure and magnetism of YFe11Ti

Self-cosistent band calculations for YFe11Ti have been performed with LMTO-ASA method in the frame of local spin density functional formalism. The electronic total energy calculations predict that the system is most stable when the Ti atoms are located at the 8f sites, while experimental results suggest the 8i sites for the Ti atoms. On the other hand, the calculated equilibrium volume of the unit cell exhibits fair agreement with the measured value. It is also shown that the unit cell volume increases with the Ti concentration, X in YFe12−XTiX, with a rate ΔV/ΔX=10 (Å3/unit cell), and the magnetic moment decreases with X with a rate ΔM/ΔX=−4μB. The total magnetic moment of YFe11Ti (X=1) is given as about 21.7μB. With a inclusion of the spin–orbit interaction in the LMTO Hamiltonian, the orbital magnetism and the magnetocrystalline anisotropy were further examined. The orbital magnetic moment per Fe atom is about 0.06μB and the anisotropy energy is obtained as 97μRy/f.u. The value leads to about 12.1×106 erg/cc, which is about the half of the measured value, 23×106 erg/cc at 1.5 K.

Theoretical Studies on the Magnetic Moments of Iron Nitrides Including Fe16N2

ABSTRACTThe spin-polarized band calculations for the iron nitrides, Fe3N, Fe4N and Fe16N2, have been performed with use of LMTO-ASA Method in the frame of local spin density functional formalism. The results show that the most distant Fe atoms from N have the largest magnetic moment. The central role of the N atom is to bring about the large magnetic moments through the lattice expansion. Concurrently, the N atoms promote an itinerancy of electrons and then in turn prevent the exchange-splitting. This results in an Fe16N2 with the lowest N concentration having the largest magnetic moments. Quantitatively, the obtained magnetic moments are in fair agreements with the experimental results except for Fe16Nr The calculated magnetic moment of Fe6N2 is about 2.4 ΜB/Pε, while the measured value is reported as 3.5 ΜB/FB. The orbital magnetic moment of Fe16N2 is about 0.07 ΜB, which is too small to make up for the difference from the experimental value.

Self-Consistent Band Calculations for YFe11Ti and YFe11TiN

The spin-polarized band calculations for YFe 11 Ti and YFe 11 TiN have been performed with the LMTO-ASA method in the frame of local spin density functional formalism. Analysis of the asphericity parameters Δ n p and Δ n d predicts that the N atoms attract the wavefunctions of Y atoms rather than of Fe atoms and in turn release the Fe atoms from bonding with Y atoms. By this effect the N atoms further increase the Fe magnetic moments besides by expanding the lattice. As for the local magnetic moments, the moments of the nearest neighbor Fe atoms to the N site are lowered with inclusion of N atoms while the furthest Fe atoms from N have the largest moments. The spin fluctuation theory developed by Mohn and Wohlfarth is shown to give a fair description to the change of the Curie temperature due to the nitrogen absorption, as well as for Y 2 Fe 17 N 3 .

Self-consistent calculations for the electronic structures of iron nitrides, Fe 3N, Fe 4N and Fe 16N 2

The spin-polarized band calculations for the iron nitrides, Fe 3N, Fe 4N and Fe 16N 2, have been performed with use of the LMTO-ASA method in the frame of local spin density functional formalism. The results show that the most distant Fe atoms from N have the largest magnetic moment. This can be ascribed mainly to the transfer of the down spin electrons, which is caused by the electronic interference due to the interstitial N atoms. The central role of the N atom is to bring about the large magnetic moments through the lattice expansion. Concurrently, the N atoms promote an itineracy of electrons and then in turn prevent the exchange-splitting. This leads to the behavior that the lower N concentration gives the larger magnetic moments. Quantitatively, the results are in fair agreement with the experimental results except for Fe 16N 2 whose measured value is considerably larger than the calculated result.

Electronic and Magnetic Structure of Fe4N

The spin-polarized band calculation for Fe 4 N has been performed with use of LMTO-ASA method in the frame of local spin density functional formalism. The calculated magnetic moments on the two unequal Fe sites are in good agreement with the experimental values reported previously. The N atom not only brings about these magnetic moments for the γ-phase Fe lattice through the magnetovolume effect, but also prevents the exchange-splitting by helping the hopping of the electrons. The down spin electrons are distributed more in face-centered Fe, FeII, than in cornered Fe, FeI. This gives the larger magnetic moment to FeI site. In addition, we have made a comparison of the charge density of an N atom in Fe 4 N and the one of a free N atom within the atomic sphere. The result indicates that the N atoms in Fe 4 N play a role of an acceptor for electrons.

Behavior of magnesium clusters under electron attachment and detachment.

Electronic-structure studies on neutral, anionic, and singly and doubly charged cationic ${\mathrm{Mg}}_{\mathrm{n}}$ clusters (n\ensuremath{\le}6) have been carried out within the local spin-density functional formalism. We present results on their equilibrium geometries and discuss their stability. We find the geometry of anionic clusters to have the same symmetry as corresponding neutral clusters. The stability of anionic clusters comes from the filling of a bonding orbital formed mainly of atomic p orbitals invariant under the symmetry group of the cluster. The calculated electron affinities are in excellent agreement with recent experimental values.

Spin-polarized electronic structures of La 2CuO 4

We have performed the spin-polarized total-energy band-structure calculation for La 2CuO 4 within the local spin density functional formalism using the semirelativistic normconserving pseudopotentials and the gaussian-orbitals basis set. An antiferromagnetic insulating state is found to be stable agaist a paramagnetic metallic state.

Electronic Structure of Impurities in Ferromagnetic Iron. III. Light Interstitials

A self-consistent calculation of the electronic structure of light impurities (µ + , H, He, …, F, Ne) at substitutional and interstitial sites in ferromagnetic iron is presented. The calculation is based on the KKR method with the impurity potential self-consistently determined by use of the local spin density functional formalism. The adiabatic potential of impurity around the center of a substitutional site is also calculated within the same framework with the result that it takes a maximum value at the center in the cases of µ + , H, B, C, N, O and F, a minimum one in the cases of He, Li and Ne and is quite flat in the case of Be. A qualitative argument is given on the mechanism underlying the variation of the adiabatic potential with atomic number. Experimental data on the hyperfine interaction of impurity nuclei are discussed in the light of these calculations to conclude plausible locations of impurities.

The electronic structure and properties of the C15 compounds CeAl 2, LaAl 2 and YAl 2

Results of self-consistent band calculations are reported for the C15 structured XAl 2 materials (X = Y, La, and Ce) using the local spin density functional formalism for assumed ferromagnetic and antiferromagnetic states as well as the paramagnetic state. The X-atoms are found to be the dominant factor is determining the electronic structure near the Fermi energy and this is enhanced by the presence of f-bands close to (LaAl 2) or at (CeAl 2) the Fermi energy. In paramagnetic CeAl 2, the f-bands are about 1 eV wide and, although principally above the Fermi energy, extend down to accomodate the additional electron compared to LaAl 2. The ferromagnetic state is found not to be stable. By contrast, the antiferromagnetic state is found to be stable with a magnetic moment of 0.88μ B per Ce atom in very good agreement with the maximum moment, 0.89μ B found in the neutron measurements of Barbara et al. A significant narrowing of the f-bandwidth is observed in the antiferromagnetic state. The antiferromagnetic spin density ordering appears to be related to nesting features in this underlying Fermi surface in LaAl 2 (i.e., no 4f electron) rather than that of CeAl 2.

Exchange interactions and spin-wave stiffness in ferromagnetic metals

Rigorous expressions for the exchange parameters and the spin-wave stiffness constant of ferromagnetic metals are obtained using a local spin-density functional formalism and the muffin-tin potential model. The calculated results for ferromagnetic iron are given as an example of the approach.

Calculation of the Electronic Structure of Positive Muon and Boron at the Tetrahedral Interstitial Site in Silicon

The spin-polarized calculation of the electronic structure around a positive muon and boron at the tetrahedral interstitial site in silicon is carried out by use of the local spin-density functional formalism and the linear combination of atomic orbitals-Green's function method. A paramagnetic solution is obtained. Bonding hyper-deep impurity states below the valence band and antibonding deep ones in the gap caused by the strong sp -hybridization between the impurity orbitals and the tails of the surrounding host orbitals appear. The calculated value of the reduction of hyperfine coupling constant, A , experienced by positive muon at absolute zero temperature is in good agreement with the experimental one. The hyperfine field of boron is predicted to be +29.72 kG. The 1 s core-polarization makes large negative contribution to the hyperfine field in the case of boron.

Electronic structure of positive muon in silicon

The spin polarized electronic structure around a positive muonμ + at the tetrahedral interstitial site of silicon is calculated by use of the LCAO-Green's function method and the local spin density functional formalism. The bonding hyper deep impurity state below the valence band and the antibonding deep one in the gap caused by the strong sp hybridization in the majority spin band give the most large contribution to the hyperfine coupling constant ofμ +. The reduction of the hyperfine coupling constant,A, experienced byμ + at absolute zero is calculated to be 0.406 in satisfactory agreement with the experimental value of 0.405 ± 0.026 or 0.450 ± 0.020.

Self-consistent calculation of hyperfine fields and adiabatic potential of impurities in iron

Hyperfine fields of impurities of the atomic number Z=1–56 at the substitutional site and those of light impurities of Z=1–9 at the interstitial sites in ferromagnetic iron are calculated by the KKR method adapted to the system containing a single impurity atom. The potential of the impurity atom is determined self-consistently by use of the local spin density functional formalism. The results for nonmagnetic sp valence impurities agree with those of the previous nonself-consistent calculation by Katayama-Yoshida, Terakura and Kanamori except for a few cases, confirming their theory of the systematic variation of hyperfine fields. The calculation for magnetic impurities of transition elements is presented for the first time in this paper. The calculations mentioned so far assume that impurities are situated at the center of each site. For the purpose of discussing the stability of the impurity positions, the change of the adiabatic potential due to displacements from the center is calculated by carrying out similar self-consistent calculations for off-center impurity positions. It is concluded that positive muon and some light impurities including boron will be displaced from the center when trapped in a vacancy.

Hyperfine interaction of light interstitial impurity nuclei in silicon

The spin-polarized electronic structure around the light impurity nuclei such as boron and positive muon at tetrahedral interstitial site of silicon is calculated by use of the local spin-density functional formalism and the LCAO-Green's function method. A paramagnetic solution is obtained, and hyper-deep impurity states below the valence band caused by the strong hybridization between the impurity orbitals and the tails of the surrounding host orbitals give large positive contribution to the hyperfine field. The Is core-polarization makes large negative contribution to the hyperfine field in the case of boron.

Pseudopotential total energy calculations for Si(111)-(1×1) and Si(111)-(2×1)

The total energies of several models of the Si(111) surface have been calculated with the pseudopotential method and the local spin density functional formalism. The 2×1 chain model has the lowest calculated total energy of those structures considered. The energy of the relaxed 1×1 geometry is minimized when the electrons in the surface states have their spins ordered with a 2×1 antiferromagnetic symmetry. Such a surface may exist on laser annealled Si(111)-(1×1).