Spin-polarized Energy Bands Research Articles

GMR in Ni/Cu multilayers: an electronic structure study

Ab initio self-consistent semi-relativistic spin-polarized TB-LMTO energy band calculations have been carried out on Ni/Cu(100) multilayers, to study the in-plane as well as perpendicular to plane giant magnetoresistance (GMR) effects. The magnetic interaction energies, evaluated as a function of layer thickness, indicate that the antiferromagnetic ordering is a possible ground state for manifestation of GMR. Using the density of states at Fermi level and the Fermi velocity, GMR has been estimated as a function of the Cu spacer thickness.

Theory of the spin dependence of the inelastic mean free path of electrons in ferromagnetic metals: A model study

We explore the spin dependence of the inelastic mean free path of an excited electron in a model ferromagnetic metal. The excited electron is assumed to reside in a plane-wave state, while the metal electrons are modeled within the framework of a one-band Hubbard model. We consider scattering by both Stoner excitations and by spin waves, and outline their relative importance in various energy ranges. In addition, we explore the dependence of the inelastic mean free path on the number of holes in the spin-polarized energy bands of the substrate.

Magnetism of FeRh1−xPdx system — band calculation

Abstract The first-principle spin-polarized energy band calculations were performed using the LMTO method in order to determine the total energy and the local moments of the body-centered tetragonal FeRh 1− x Pd x alloys as a function of the axial ratio c a from 0.8 to 1.358. The calculations show that there are competing ferromagnetic and antiferromagnetic states in FeRh alloy with c a =1 and in FeRh 0.5 Pd 0.5 alloy with c a =1.238 . The first-order magnetic transitions can therefore be induced at finite temperatures as have been observed experimentally in both alloys.

Self-consistent antiferromagnetic ground state for La2CuO4 via energy-band theory.

We have used the pseudofunction method to compute self-consistent spin-polarized energy bands for ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$. The ground state is found to be semiconducting and antiferromagnetic (AF) with a moment of 0.35${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$. The net moment resulting from the occupation of 82 itinerant bands is localized on the Cu atoms only. Our results agree with experiments in which ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$ is found to be semiconducting and AF with a moment on the Cu atoms of (0.35\ifmmode\pm\else\textpm\fi{}0.05)${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ (neutron scattering) or in the range 0.2${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ to 0.6${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ (muon-spin resonance). Sr is found to produce holes on the out of plane O contrary to the assumption used in many strong-correlation theories of superconductivity.

Ground state properties of the AnFe 2 systems (An = U, Np and Pu)

We report on spin polarized energy band calculations for the series AnFe 2 (An = U, Np and Pu) in which both spin-orbit coupling and splitting of the energies of the 5f orbital polarization are included self-consistently. The new feature of the magnetism is the existence of large orbital moments on the actinide sites. The calculated moments agree with experiment. Finally we compare with published neutron diffraction results for the actinide 5f form factor of UFe 2 and PuFe 2, obtaining agreement with experiment and predict the form factor of NpFe 2.

Binding energy and magnetism of transition metal hydrides

Self-consistent density functional calculations for nickel and manganese hydrides are reported. The linear muffin-tin orbital (LMTO) method was used to calculate spin-polarized energy bands for several lattice constants and crystal structures. Total energies have been calculated and the importance of the Madelung energy has been demonstrated.

Spin-Polarized Energy Bands of UFe2

The spin-polarized energy bands, density of states and calculated equation of state of UFe2 are analysed. The calculated lattice parameter is in good agreement with experiment and both the iron 3d and uranium 5f electrons are found to be strongly bonding. Hence we conclude that the uranium 5f electrons are hybridizing with both iron 3d and other conduction electrons. In the spin-polarized calculations a self-consistent moment of 0.7 μB on an iron site was obtained, in reasonably good agreement with the experimental value of 0.6 μB. However, on the uranium site a moment of -0.6 μB was calculated in apparent conflict with the experimental value of 0.06 μB. The anomaly is attributed to the effect of spin-orbit coupling.

Electronic Structure and Antiferromagnetism in La2CuO4

ABSTRACTSelf-consistent spin-polarized energy bands have been calculated for tetragonal and orthorhombic La2CuO4. No stable antiferromagnetic order is found in either the stoichiometric compound or oxygen deficient La2CuO3.75. Constraining the occupancy of Brillouin zone boundary states leads to a small antiferromagnetic moment in both systems which is rapidly quenched by Ba doping.

Binding mechanism and itinerant magnetism of ZrFe 2 and YFe 2

Self-consistent spin-polarized energy band calculations for the two Laves phases show that a ferrimagnetic state is more stable than the paramagnetic one, but at a slightly larger volume. For ZrFe 2 the interaction between the low lying Zr and the exchange-split Fe states leads to covalent magnetism which is discussed using site- and spin-projected densities of states. The different interaction between Fe and Zr for majority and minority spin is responsible for the ferrimagnetic ordering which is analyzed in terms of spin densities. The resulting magnetic moment of about 1.9 μ B for Fe is spatially localized near the Fe site, while around Zr a small but extended negative spin density causes (through the large volume) a moment of about -0.56 μ B a prediction which should be verified experimentally. YFe 2 is qualitatively similar, but contrasts YCo 2 which is near a possible metamagnetic transition.

Large Orbital-Moment Contribution to5fBand Magnetism

It is calculated that spin-orbit coupling induces a predominant orbital magnetic moment ($\ensuremath{-}1.5{\ensuremath{\mu}}_{\mathrm{B}}$) antiparallel to the spin moment ($1.0{\ensuremath{\mu}}_{\mathrm{B}}$) in the spin-polarized energy bands of UN. The shape of the magnetic form factor, pressure dependence of the moment, and presence of large magnetic anisotropy then become compatible with itinerant-electron theory.

Electronic structure and magnetism of surfaces and interfaces

Spurred by recent experimental advances, theoretical/computational methods for accurately determining the electronic structure and properties of surfaces and interfaces have been developed. This paper reviews the advanced state of local spin density determinations of the magnetic properties of free surfaces (e.g. Ni and Fe) and interfaces (e.g. Ni on Cu), using self-consistent spin-polarized energy band calculations of the energy dispersion and spatial character of surface and interface states.

Theoretical determination of exchange splittings for ferromagnetic metals: Effects of a nonlocal spin density exchange potential

We present preliminary results of a self-consistent spin polarized energy band calculation for Ni using a nonlocal exchange potential based on the weighted density approximation of Gunnarsson et al. and a local correlation potential of Vosko et al. The exchange splitting (0.4 eV) is much closer to the experimental measurements (0.3 eV) than that predicted by the local density theory (0.6 eV).

Spin-polarized electronic structure of the Ni(001) surface and thin films

Spin-polarized energy bands, charge and spin densities have been calculated self-consistently for one, three, and five atomic (001) layers of fcc Ni using the linear augmented plane-wave method and the von Barth---Hedin approximation for exchange and correlation. The self-consistent potential of the five-layer film is used to calculate the electronic structure of a 13-layer film. The theoretical work function of 5.4 eV agrees well with the experimental value of 5.2 eV. The calculated spin moments are ordered ferromagnetically in all the films considered, and the moments of the atoms in the surface layer are 0.95, 0.69, and 0.65 Bohr magnetons for the one-, three-, and five-layer films, respectively. The moment of an atom in the central layer of the five-layer film is 0.61 Bohr magnetons as compared with the calculated (experimental) bulk value of 0.59\ifmmode\pm\else\textpm\fi{}0.01 (0.56) Bohr magnetons. The increase of the magnetic moment at the surface is mainly of $d({x}^{2}\ensuremath{-}{y}^{2})$ character. The calculated $4s$ contribution to the hyperfine field changes sign and becomes positive in the outermost layer. Near $k=0$, between the Fermi level and the $d$-band edge (which lies 0.3 eV below the Fermi level), we find no majority-spin surface states that can explain the sign reversal of the electron spin polarization near threshold. This supports the suggestion by Liebsch that, in photoemission experiments on Ni, correlation effects make the majority-spin bands appear higher in energy. With such an adjustment of our energy bands we are able to identify the two spin-up $\overline{\ensuremath{\Sigma}}$ surface bands, but not the ${\overline{\ensuremath{\Delta}}}_{1}$ band, observed in angular-resolved photoemission experiments.

Calculation of the spin-polarized energy-band structure of LaNi5and GdNi5

Spin-polarized energy bands, the density of states, and the magnetic moments are calculated for the intermetallic compounds La${\mathrm{Ni}}_{5}$ and Gd${\mathrm{Ni}}_{5}$ with the use of the self-consistent augmented-plane-wave method. The calculations reveal a charge transfer of 1.5 electrons from La to Ni but no charge transfer from Gd to Ni. The calculated width of the $3d$ band and the calculated electronic specific-heat coefficient for La${\mathrm{Ni}}_{5}$ are in good agreement with the ultraviolet photoelectron spectroscopy results and measured electronic specific-heat data.

Magnetism of surfaces and interfaces

Recent experimental advances in the study of surfaces have raised important questions about our fundamental understanding of these phenomena. One important consequence of this has been the development of theoretical/computational methods for accurately determining the electronic structure and properties of surfaces and interfaces. This talk reports on theoretical determinations of the magnetic properties of free surfaces [e.g., Ni(110)] and overlayers [e.g., Ni on Cu(001)] based on self-consistent spin polarized energy band determinations of the energy dispersion and spatial character of surface states. Particular attention is paid to surface state effects on surface spin polarization, magnetic moments, and exchange splittings. Detailed results of charge and spin densities and layer projected density of states are presented. Comparisons are made to relevant photo-emission and other experiments, the nonexistence of magnetically ’’dead’’ layers is described, and comparisons with earlier results1 on coherent modulated Cu/Ni structures are given.

Metamagnetism of palladium

Abstract Self-consistent spin-polarized energy band studies with the applied magnetic field included, show Pd metal to undergo a metamagnetic transition in high magnetic fields. The calculated moments and susceptibilities are found to be greatly enhanced for tetragonally (“stretched”) Pd as in the Au/Pd/Au sandwiches studied by Brodsky and Freeman and to indicate the possibility of ferromagnetism in tet. Pd.

Self-consistent spin polarized energy band structure and magnetism in ZrZn 2 and TiBe 2

Results of self-consistent spin-polarized semirelativistic linear muffin-tin orbital energy band studies of TiBe 2 and ZrZn 2 are reported. The calculated magnetic moments, spin magnetization densities and neutron magnetic form factors - and their comparison with experiment - are used to discuss itinerant ferromagnetism in ZrZn 2 and TiBe 1.8Cu 0.2.

Spin-polarized energy-band structure of YCo5, SmCo5, and GdCo5

The spin-polarized electronic energy bands, densities of states, and magnetic moments of the intermetallic compounds Y${\mathrm{Co}}_{5}$, Sm${\mathrm{Co}}_{5}$, and Gd${\mathrm{Co}}_{5}$ are calculated by a self-consistent augmented-plane-wave method. The results are similar in the three cases, with the computed magnetic moments in reasonable agreement with experiment. Only about one electron (of a possible three) is transferred from the rare earth to cobalt, leaving the minority-spin cobalt $3d$ band unfilled, and the moment high. There is evidence of $d\ensuremath{-}d$ coupling between cobalt and the rare earth, providing information as to why experiments designed to reverse the antiparallel spin coupling between the two sublattices by manipulation of the electron concentration have been unsuccessful.

Theoretical estimation of the band and coulomb parameters in K +TCNQ −

Spin-polarized energy band structures show that correlation effects may be responsible for the observed semiconductive properties of the potassium salt of 7,7', 8,8'-tetracyanoquinodimethan (K +TCNQ −). The one-electron bandwidths calculated are comparable with the effective Coulomb repulsion suggesting the intermediate- to strong-coupling scheme as appropriate to this crystal.

Spin-Polarized Energy Bands in Eu Chalcogenides by the Augmented-Plane-Wave Method

Spin-polarized energy bands in the Eu chalcogenides have been obtained by the augmented-plane-wave (APW) method. The $4f$ band positions are extremely sensitive to the exchange potential used. A reduced exchange parameter of $\frac{3}{4}$ for the magnetic ${\mathrm{Eu}}^{2+}$ ions has produced proper energy gaps and relative $f$ band positions for EuO, EuS, and EuSe. We have obtained the $f(\ensuremath{\uparrow})$ bandwidth as about 0.5 eV and the up- and down-spin $f$ band separation as about 6 eV. We have also obtained anion $p$ bandwidths of about 2 eV which are almost constant for the Eu chalcogenides. The calculated density of states agrees qualitatively with photoemission data, except for the experimental density of states of the $4f(\ensuremath{\uparrow})$ band which has a large bandwidth of about 1.5 eV. The probable causes of this discrepancy are multiple scattering of the $4f$ electrons with phonons and electrons, or recombinations with ${\mathrm{Eu}}^{3+}$ ions. The observed absorption-edge red shifts are due to the spin-polarized exchange splitting $\ensuremath{\Delta}{E}_{\mathrm{ex}}$ of the lowest conduction band ${X}_{3}$. Estimated $\ensuremath{\Delta}{E}_{\mathrm{ex}}$ values are 0.4-0.5 eV for Gd metal and Eu chalcogenides. The $f(\ensuremath{\uparrow})$ bands in Eu and Gd metals are expected to be located within 3 eV below the Fermi level. The high-energy reflectivity data, effective masses, possible conduction mechanism, and APW charge analysis have been discussed.