Itinerant Band Research Articles

Magnetic interactions in the metallic phase of the copper oxides

The CuCu spin interactions arising from a mediating itinerant oxygen band is derived. Using a formalism similar to that which has been applied to heavy fermion metals, we solve for the concentration dependence of both superexchange and RKKY interactions. The former falls off dramatically with increasing dopant concentration, while the latter undergoes a sign change.

RVB-Itinerant P Hole Model for High-Tc Copper Oxides

A model for the high-Tc Copper Oxides is studied. The localized nature of Cu 3d electrons is described as the RVB quantum spin liquid and the doped O 2p holes are described with an itinerant band. Our analysis shows that the virtual exchange of two spinons induces a pairing interaction between two holes.

High field magnetization of 3d transition metal intercalates M xTiS 2 (M = 3d metals)

High field magnetization has been measured on the single crystals of 3d transition metal intercalates M x TiS 2 (M = Mn, Fe, at 4.2 K in pulsed fields up to 36 T. In particular, Fe x TiS 2 shows a strongly anisotropic hyteresis curve with easy axis parallel to the c-axis, while other intercalates have a paramagnetic behavior. These magnetic properties are understood reasonably in the light of an itinerant electron model or band picture.

Itinerant magnetic character in 3d transition-metal intercalation compounds MxTiS2

The magnetization and specific heat data, together with the transport and photoemission data, of 3d metal intercalation compounds MxTiS2 with the 1T-CdI2 type layered structure, show that an itinerant electron or band picture is valid in this material system, in agreement with band calculations using a self-consistent APW method.

Electrical and thermal properties of intercalation compound FexTiS2

Intercalation phenomena of guest Fe atoms into van der Waals gaps of the host 1T - TiS2 layered crystal have been studied by transport measurements. These experimental results, together with other data, are indicative of the presence of spin-up and spin-down bands produced by the host-guest interactions and understood in terms of an itinerant band picture, in agreement with recent band calculations.

ChemInform Abstract: Superconductivity and Lattice Parameters in (La1‐xSrx)2CuO4‐δ Solid Solution System.

ChemInformVolume 18, Issue 46 Physical Inorganic Chemistry ChemInform Abstract: Superconductivity and Lattice Parameters in (La1-xSrx)2CuO4-δ Solid Solution System. S. KANBE, S. KANBE Dep. Chem., Helsinki Univ. Technol., SF-02150 Espoo, Finl.Search for more papers by this authorK. KISHIO, K. KISHIO Dep. Chem., Helsinki Univ. Technol., SF-02150 Espoo, Finl.Search for more papers by this authorK. KITAZAWA, K. KITAZAWA Dep. Chem., Helsinki Univ. Technol., SF-02150 Espoo, Finl.Search for more papers by this authorK. FUEKI, K. FUEKI Dep. Chem., Helsinki Univ. Technol., SF-02150 Espoo, Finl.Search for more papers by this authorH. TAKAGI, H. TAKAGI Dep. Chem., Helsinki Univ. Technol., SF-02150 Espoo, Finl.Search for more papers by this authorS. TANAKA, S. TANAKA Dep. Chem., Helsinki Univ. Technol., SF-02150 Espoo, Finl.Search for more papers by this author S. KANBE, S. KANBE Dep. Chem., Helsinki Univ. Technol., SF-02150 Espoo, Finl.Search for more papers by this authorK. KISHIO, K. KISHIO Dep. Chem., Helsinki Univ. Technol., SF-02150 Espoo, Finl.Search for more papers by this authorK. KITAZAWA, K. KITAZAWA Dep. Chem., Helsinki Univ. Technol., SF-02150 Espoo, Finl.Search for more papers by this authorK. FUEKI, K. FUEKI Dep. Chem., Helsinki Univ. Technol., SF-02150 Espoo, Finl.Search for more papers by this authorH. TAKAGI, H. TAKAGI Dep. Chem., Helsinki Univ. Technol., SF-02150 Espoo, Finl.Search for more papers by this authorS. TANAKA, S. TANAKA Dep. Chem., Helsinki Univ. Technol., SF-02150 Espoo, Finl.Search for more papers by this author First published: November 17, 1987 https://doi.org/10.1002/chin.198746012AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume18, Issue46November 17, 1987 RelatedInformation

Magnetic properties of Y-Ba-Cu-O superconductors.

The magnetic properties of polycrystalline and single-crystal samples of YBa/sub 2/Cu/sub 3/O/sub 7/ are compared. Transition temperatures are in the range of 85 to 89 K. The Meissner effect is below 30% of the diamagnetic shielding in all cases. Based on the high-temperature susceptibility it is suggested that an itinerant antiferromagnetic 3d band of the Cu/sup 2+/ is possible. Anisotropy occurs in the single crystal for applied fields above 200 Oe. There is a difference in the lower critical field of a factor of 20 where H/sub c//sub 1/ is about 4000 Oe for H parallel to the orthorhombic c axis and 200 Oe for H perpendicular to the c axis of the crystal.

Superconductivity and Lattice Parameters in (La1−xSrx)2CuO4−δ Solid Solution System

Abstract The superconducting critical temperature TC increased with increase in x in (La1−xSrx)2CuO4−δ associated with the shortening of the Cu–O bond in the basal plane and the elongation of the lattice along the c-axis in the K2NiF4. structure. The results are discussed in terms of two-dimensional itinerant band formation of Cu:dx2-y2–O:pσ bond.

Electrical properties and stoichiometry in La 2NiO 4

The electrical properties of La 2NiO 4 have been studied with respect to the stoichiometry of the material. The conductivity of reduced compositions has been measured between 20 and 1000 K and compared to that of the air-prepared ones. Nonstoichiometry is present in both cases and produces disorder leading to Anderson localization and to the definition of a mobility edge in the σ x 2− y 2 itinerant band. Air-prepared compounds contain in addition a large number of Ni 3+ states which may overlap the itinerant σ x 2− y 2 band. For reduced materials containing small amounts of Ni 3+, the electrical properties can be described below 200 K by a hopping conductivity at the Fermi level within a sharply peaked density of states. The results are well described within the frame of the Mott theory of variable range hopping. Above 200 K highly reduced materials exhibit direct excitation of holes from Ni 3+ states to the mobility edge in the itinerant band. Under conditions appropriate to air-prepared materials, the Fermi level is shifted toward the itinerant band and a major contribution to the conductivity arises from hopping at the Fermi level. At high temperature a progressive excitation of carriers from the localized states is anticipated with an eventual exhaustion region. This last assumption is corroborated with a shift of the conductivity maximum to higher temperature for increasingly reduced materials.

Should the Davis-Bacon act be repealed?

F ifty-two years ago Congress passed the Davis-Bacon Act in order to correct a serious labor abuse caused by two factors: a huge federal construction program and a chaotic labor market. Unscrupulous contractors were winning government contracts by employing itinerant bands of unskilled laborers and paying them exploitive wages. This widespread practice had two results: it took contracts away from local contractors, and it resulted in work of lower quality since the laborers were, at best, only marginally skilled. The Davis-Bacon Act successfully corrected this abuse. Today, however, it is questionable whether the Act is viable and effective under current economic conditions, and a move is clearly afoot to repeal the Act or to amend it radically. The champion of the Act is organized labor-primarily the Building and Construction Trades of the AFL-CIO-in tandem with the Department of Labor. Together they have joined to provide almost every word in defense of the Act. The foes of Davis-Bacon are far more diversified and include nine separate Government Accounting Office reports, a Carter administration Office of Management and Budget report, and a report by the Congressional Budget Office, to name only a few. 1 As could be expected, management organizations, such as the Associated General Contractors and the U.S. Chamber of Commerce, are also quite vocal in their support for repeal. It is interesting to note that no professional economists have testified in favor of the Davis-Bacon Act. 2 Ultimately the fate of the Davis-Bacon Act will be decided by Congress, not necessarily as a result of a rational decision about what is right or wrong, effective or obso-

Electron transport and magnetic properties of La 1− xSr xCo 1− yTi yO 3 ( x = 0 a or x = yb)

The two systems (a) and (b) for different values of x were synthesized. Their electron transport and magnetic properties show a change in behavior above a critical value of x. Unlike the system La 1− x Sr x CoO 3, itinerant electron ferromagnetism is not observed. This is explained on the basis of the absence of an itinerant band of Co 4+ whose generation is restricted on account of substitution of Ti 4+. Electron transport in these two systems is compared with that of LaCoO 3 or La 1− x Sr x CoO 3 and is discussed in view of the presence of different valence states of cobalt and change in crystal field splitting. Spin-state equilibria in these two systems are similar to that in LaCoO 3.

Superconductivity and magnetism in Y4Co3 (invited)

Y4Co3 is the first itinerant band magnetic superconductor. Experimental results suggest that magnetism and superconductivity in this compound are strongly linked. This may be due to strongly hybridized Y–Co bands.

Chemisorption and the initial stage of oxidation on Mn

Chemisorption of O 2, CO, and N 2 on clean manganese has been studied by the techniques of X-ray and UV photoelectron spectroscopy (XPS and UPS) and active ion bombardment and modeled by means of the empirical bond energy-bond order (BEBO) approach. O 2 adsorbs dissociatively and the initial monoxide formation begins at 2 L exposure. MnO is identified by the transition of the itinerant Mn 3d metallic band to the localized discrete ionic 3d state of Mn 2+ and by the splitting of the Mn 2p 1 2 , 3 2 core lines into two components. CO adsorbs in both the dissociative and molecular forms, with the two species co-existing on the surface and distinguishable by the atomic or molecular nature of the valence states and the splitting of the O 1s and C 1s core lines. N 2 adsorbs dissociatively and only after a small activation energy is supplied, e.g., by means of bombardment with N 2 +. The BEBO model is in agreement with and provides an interpretative approach to the chemisorption results.

Abstract: Electronic and magnetic properties of nickel as described using experimental spin-split energy band dispersions

Angle-resolved photoemission studies of Ni (111) and Ni (100) crystals, used to determine energy-vs-momentum s- and d-band dispersions, show that ferromagnetic nickel can be described by a spin-split itinerant band model with an exchange splitting. An experimental one-electron energy band model for Ni gives a consistent description of various electronic and magnetic properties including Fermi surface radii, spin-polarized field emission and photoemission data, Bohr magneton number and optical properties. (AIP)

Itinerant-3d-electron spin-density oscillations surrounding solute atoms in Fe

A previous method of analysis of hyperfine-field spectra of dilute Fe-based alloys with transition solute atoms to the right of Fe in the periodic table is extended to obtain the solute- and host-moment perturbations of dilute Fe-based alloys with any $3d$ or $4d$ transition element. The resulting host-moment perturbations show very simple oscillatory behavior which can be interpreted as due to spin density oscillations in the itinerant $d$ electrons. It is shown that these spin density oscillations can be thought of as arising from the polarization induced in the itinerant $d$ electrons by the localized $d$ moment via mainly Coulomb exchange interactions, whereas the localized moments arise from the intra-atomic exchange interaction between the localized $d$ electrons. Within this scheme a purely itinerant band ferromagnetism is not plausible. The value of the Curie temperature of Fe is shown to be in good agreement with the interpretation. The features that are important in determining alloy behavior are clearly seen in this analysis and are enumerated and discussed. The contrast in behavior with dilute Ni-based alloys is also briefly discussed.

Conduction band behaviour in antiferromagnetic semiconductors

The interaction of itinerant conduction band electrons with the localized spins of an antiferromagnetic lattice is investigated in the spin-wave approximation. The interaction results in: (a) removal of the spin and site degeneracy of the atomic levels; and (b) the appearance of an effective resonance energy of two neighbouring sites. The thermal average of the latter suggests a non-exponential dependence on the temperature and coupling strength, in contrast to the earlier studies of Wolfram and Callaway (1962).

Magnetic properties of NiCr alloys

AbstractNew magnetization measurements on NiCr alloys are reported. At increasing Cr concentrations c less than 11 at%, the mean atomic moment M0 = 0 for c = 12 at% Cr. In the critical concentration range, 11 < c < 15 at% Cr, the experimental data are analysed in terms of the itinerant band model of very weak ferromagnetism. Several characteristic properties related to the effective exchange interaction and to the band structure near the Fermi level are deduced from this analysis.