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  • 1
    Electronic Resource
    Electronic Resource
    Antiferromagnetic interlayer coupling in Fe/V and Fe/Cr : 35th annual conference on magnetism and magnetic materials (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 4544-4546 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Antiferromagnetic (AF) coupling between Fe and V atoms is observed experimentally at the Fe/V and Fe/Cr interfaces. In the self-consistent tight-binding derivation of the unrestricted approximation of the Hubbard Hamiltonian, we have investigated Fe3Vn (n=1–5) superlattices and Fe3Vn (n=1–5) films. In all cases one finds an AF coupling between Fe and V together with a decreasing oscillation of the induced magnetic moment on the V atoms when the distance from Fe increases. The distributions of local magnetic moments on Fe and Cr layers in Fe3Crn (n=3–5) superlattices have been determined self-consistently. Both AF and ferromagnetic (F) coupling between Fe layers separated by Cr have been studied. In all cases one finds strong AF couplings between Fe and Cr nearest neighbors with an important increase of the Cr magnetic moment at the interface as compared to the Cr bulk value.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348354
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  • 2
    Electronic Resource
    Electronic Resource
    Vanadium: From cluster to semi-infinite crystal : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6207-6209 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Antiferromagnetic coupling between nearest neighbor vanadium atoms is discussed in the case of free-standing cluster and slabs, steps at the surface of V and V islands on Ag(001). In the self-consistent tight-binding derivation of the unrestricted approximation of the Hubbard–Hamiltonian, we have investigated the onset of magnetism in terms of the exchange integral J. For each topological arrangement of the V clusters [free-standing or as overlayer on Ag(001)], various possible magnetic states are considered and transition from nonmagnetic to magnetic order is characterized. The (001) surface is shown to present magnetism for a value of J lower than those for the other crystallographic faces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352699
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  • 3
    Electronic Resource
    Electronic Resource
    A mass formula for 4He clusters (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 7335-7341 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An analytic expression for the total energy of 4He clusters composed of N atoms is obtained by means of a variational solution of the energy density functional. The energy is calculated as an expansion in decreasing powers of the cluster radius, R∝N1/3. Contributions of volume (R3), surface (R2), curvature (R), constant (R0), (1/R), and (1/R2) are clearly separated in the formula. Chemical potentials, fusion and fission potentials, surface thickness, and unit radii are also obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460217
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  • 4
    Electronic Resource
    Electronic Resource
    Antiferromagnetic versus ferromagnetic coupling in Fe/Cr(107) and Cr/Fe(107) : The 6th joint magnetism and magnetic materials (MMM)-intermag conference (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 6989-6991 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have calculated the local magnetic moments and magnetic order for a Fe(Cr) monolayer adsorbed on a stepped Cr(Fe)(107) substrate. The electronic structure at T=0 K has been self-consistently determined within the unrestricted Hartree–Fock approximation of the Hubbard Hamiltonian in the framework of a real-space tight-binding method. In the Cr/Fe(107) system, two magnetic arrangements have been obtained, the more stable being the less frustrated as obtained in the case of V overlayers on vicinal substrates of Fe. An analysis of both solutions in terms of the total energy calculation and the different degree of frustration is presented. For Fe/Cr(107), a two-step periodicity is obtained. The sign of the magnetization at the Fe overlayer changes from step to step. This spin-flop transition is consistent with the two-layer period oscillation recently observed in Fe/Cr/Fe wedge structures, and with the total magnetization determined from in situ magnetometer measurements during growth of ultrathin Fe films on Cr(001).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358529
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  • 5
    Electronic Resource
    Electronic Resource
    Geometrical and chemical environment effects on the magnetism of stepped surfaces of V and V over Fe (1993)
    Springer
    Czechoslovak journal of physics 43 (1993), S. 1045-1050 
    Details
    ISSN: 1572-9486
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract By means of a real-space tight-binding calculation we obtain the spin-polarization of vicinal (1, 0, 2n−1) vanadium surface, and of one V layer deposited on vicinal (1, 0, 2n−1) iron surfaces (n=1,2,3,4). These geometries can be viewed as a staircase on the (001) surface with steps of monoatomic height andn-atoms width. Forn≤2, the pure V stepped surfaces do not show magnetism which is consistent with the absence of spinpolarization at the (101) surface. By contrast, magnetism is always obtained when a V monolayer is deposited on Fe stepped substrate, which is due to the hybridization of d-orbitals of V and Fe. Furthermore, in all the cases where magnetism is obtained, the surface V atoms at the edge of the step result to be antiferromagnetically coupled with all kink atoms. The effect of this local defect on the magnetic structure seems to remain when approaching the (001) surface (n→∞).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01595301
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  • 6
    Electronic Resource
    Electronic Resource
    Magnetic properties of 3d-transition-metal alloy clusters: (Fe x Cr1−x ) n (1991)
    Springer
    The European physical journal 19 (1991), S. 263-265 
    Details
    ISSN: 1434-6079
    Keywords: 36.40. + d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present results for the magnetic properties of (Fe x Cr1−x ) n alloy clusters obtained by using a tight-binding Hubbard Hamiltonian in the unrestricted Hartree-Fock approximation. The dependence of the average magnetic moment, local magnetic moments, magnetic order, and cohesive energy on the size and composition of the cluster were determined. In agreement with surface calculations, we find that the average magnetic moment of the alloy is larger than that of the cluster of one element. Forn=15 a transition from ferromagnetic to antiferromagnetic order is obtained forx≈0.4−0.53. We discuss the importance of the overlap interaction in the spin polarized charge distribution of the alloy (e.g., charge transfer, local magnetic moments). The characteristic properties of the mixed clusters are also discussed by comparison with available results for homogeneous clusters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448307
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  • 7
    Electronic Resource
    Electronic Resource
    Photoabsorption cross sections of sodium clusters: electronic and geometrical effects (1993)
    Springer
    The European physical journal 26 (1993), S. 284-286 
    Details
    ISSN: 1434-6079
    Keywords: 73.20.Mf ; 36.40.+d ; 31.20.Sy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We study the origin of the discrepancy between the photoabsorption cross sections of small jellium spheres calculated by the time dependent local density approximation (TDLDA) and experiments for small metallic clusters. We have specifically studied Na 21 + . We conclude that both non-local exchange-correlation effects beyond the LDA and geometrical effects beyond the jellium approximation should be taken in the same calculation. We also present local and non-local calculations for Na n − (n=19, 91 and 197) within the framework of the jellium model. The large anions show a fragmentation of the plasmon due to its interference with the ionization threshold. This feature is absent in the TDLDA results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01429170
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  • 8
    Electronic Resource
    Electronic Resource
    Semiclassical variational study of size effects in neutral and charged jellium droplets (1991)
    Springer
    The European physical journal 19 (1991), S. 55-58 
    Details
    ISSN: 1434-6079
    Keywords: 36.40 ; 31.20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An analytic expression for the total energy of metallic clusters composed ofN identical atoms of valencev and with net chargeQ is obtained by means of a variational solution of the Thomas-Fermi-Weizsäcker energy density functional within the spherical jellium model. The minimum energy is given as an expansion in decreasing powers of the cluster radiusR=r s Z 1/3, withZ=vN andr s the radius per electron of the bulk metal. The coefficients are obtained as functions ofr s . Terms of volume (R 3), surface (R 2), curvature (R), constant (R 0), (1/R) and (1/R 2) are clearly separated in the formula, as well as the different contributions (kinetic, coulombic and exchange-correlation) to each of them. The asymptotic values (R→∞) for the work functions,W(r s ), and surface energies σ(r s ), are compared to analogous semiclassical and Kohn-Sham calculations of jellium-like surfaces and to the experimental values. The size dependent behaviour of chemical potentials, μ(R), electron affinities,AF(R), and ionization potentials,IP(R), are easily obtained for any kind of metallic clusters. In particular we discuss the Coulomb and quantum corrections to the coefficients β, δ in the asymptotic formulae:IP≃W+β/R andAF≃W+δ/R.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448254
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  • 9
    Electronic Resource
    Electronic Resource
    Response properties of sodium clusters within a jellium-like model with finite surface thickness (1991)
    Springer
    The European physical journal 19 (1991), S. 93-96 
    Details
    ISSN: 1434-6079
    Keywords: 36.40 ; 71.45.G
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The usual spherical jellium model of alkaline clusters is generalized to allow for a finite surface thickness in the positive background distribution. Static (relative stability, ionization potentials) and response properties have been calculated and the results show a better agreement with experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448263
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  • 10
    Electronic Resource
    Electronic Resource
    Optical response of bimetallic Li x Na8−x (0≦x≦8) and of doped Na8Zn clusters (1994)
    Springer
    The European physical journal 31 (1994), S. 269-273 
    Details
    ISSN: 1434-6079
    Keywords: 36.40 ; 31.15 ; 31.20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Using the time dependent local density approximation we calculate the photoabsorption spectra of bimetallic Li x Na8−x (0≦x≦8) and of doped Na8Zn clusters. Ground state cluster geometry and electronic structure are obtained by minimization of total energy from Kohn-Sham self-consistent calculations within the spherically averaged pseudopotential method. For Li x Na8−x clusters we obtain two nearly isomeric geometries. In both cases the corresponding photoabsorption spectra show a single collective excitation (surface plasmon) at increasing frequency as the number of lithium atoms increases. For a given number of lithium atoms, the plasmon frequency of the cluster in the ground state geometry is ∼0.1 eV blueshifted with respect to that in the isomeric state. The equilibrium geometry of doped Na8Zn cluster is formed by a nearly spherical shell of eight Na atoms enclosing the Zn impurity at the cluster center. The corresponding optical spectrum shows two peaks at higher frequencies than the surface plasmon of pure Na8 cluster, in agreement with recent photodepletion spectroscopy experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01445005
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