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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5194-5196 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For partially delocalized correlated f-electron systems, the key aspect of the electronic behavior is the hybridization of f electrons with the non-f-band electrons. This gives unusual properties including suppressed crystal-field splitting and highly anisotropic ordered magnetism. To improve the general understanding and to make the theory materially predictive, a technique is being developed to evaluate absolutely the parameters of the correlated electron model Hamiltonian, and then to use these to predict observed phenomenology including details of magnetic ordering such as magnetic structures and transitions between structures. The most difficult quantity to predict is the magnetic ordering temperature, among other reasons because it depends on the hybridization strength in a highly nonlinear way. Previously Wills and Cooper have reported on a technique involving a nonconventional electronic structure calculation based on treating the f electron as a resonant state in a solid-state environment to evaluate the hybridization. As an independent check on the evaluation of hybridization, here a conventional tight binding parametrization scheme was used to evaluate the hybridization. These results are compared both with previous results and with experiment for the magnetic ordering temperature and crystal-field dressing of Ce compounds, and the situation introduced by the relative degrees of nonlinearity for the crystal-field and magnetic ordering response to the hybridization strength are commented on.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5424-5426 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The isostructural uranium monopnictides and monochalcogenides have become prototype systems in actinide research with respect to their unusual magnetic properties. We have investigated the origins in the electronic structure of the variation in magnetic behavior as the degree of 5f-electron localization changes from localized to itinerant on going up the pnictogen or chalcogen column, thus decreasing the U-U separation. We have applied a synthesis of: (1) A phenomenological theory of orbitally driven magnetic ordering which includes both the hybridization-induced and the RKKY exchange interactions on an equal footing, and (2) Ab initio electronic structure calculations, based on the linear-muffin-tin-orbital method, allowing a first-principles evaluation of the parameters entering the model Hamiltonian. We have investigated systematically characteristic trends and changes of the 5f-state resonance width, the hybridization potential, and the hybridization-induced and RKKY exchange interactions with chemical environment, on going down the pnictogen or chalcogen column and on going from the weakly hybridizing pnictides to the more strongly hybridizing chalcogenides.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 5475-5477 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A synthesis of ab initio linear-muffin-tin-orbital (LMTO) electronic structure calculations and a phenomenological model of orbitally driven magnetic ordering has been applied to investigate trends of the effect of hybridization of moderately delocalized f electrons with band electrons on the diverse magnetic behavior across the cerium monochalcogenide series. The parameters entering the Anderson lattice model Hamiltonian are determined from total-energy supercell warped-muffin-tin LMTO calculations with zero, one, and two electrons in the cerium 4f core state. The origins, in the electronic structure, of the variation of the density of states at the Fermi energy, the f-state resonance width, the hybridization potential, the hybridization-dressed crystal-field splitting, and the hybridization-mediated exchange interactions with the chemical environment (anion size) on going down the chalcogen column have been investigated systematically, increasing thus the degree of f-electron localization as the cerium-cerium separation increases.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5837-5837 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have shown theoretically, by means of a full-potential LMTO method in a slab geometry, that the topmost surface layer of α-Ce is γ-like. The calculations are fully relativistic and include all electrons. Also an orbital correction to the f-electron states is included to allow for f localization. For the topmost layer the spin moment is found to be 0.70 μB for the f electrons and 0.08 μB for the d-electron states while the orbital moment from the f electrons is found to be −1.07 μB. These moments correspond well to the moments calculated for bulk γ-Ce which are 0.63, 0.07, and −0.87 μB, respectively. The subsurface and lower lying layers are calculated to have spin and orbital moments close to zero. We therefore conclude that the topmost layer on the α-Ce surface is γ-like while the subsurface and lower lying layers are similar to bulk α-Ce. Our findings explain recent photoemission experiments on this material and provide a theoretical foundation for the interpretation of these experiments. The fact that our theory assumes that α-Ce has delocalized f electrons, and the agreement with the interpretation of photoemission experiments, gives support that the Mott transition model for the α→γ phase transition is correct. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: By combining MCXD experiments with first principles electronic structure calculations, we demonstrate that the orbital contribution to magnetism can be strongly enhanced at surfaces. This effect is illustrated for Co grown on a Cu(100) surface. The MCXD measurements were performed using the SX 700 plane grating monochromators at BESSY. The Co films were evaporated and characterized in situ, for their cleanness, thickness (1.6–50 ML), and structural order. For a film thickness up to 2.2 ML, measurements of the ac MCXD susceptibility response at a fixed photon energy allowed one to measure the critical temperature, Tc, of the films and their critical properties were characterized in situ. For several samples the MCXD response as a function of the x-ray incidence angle was investigated as well. This allows one to quantify and correct saturation effects that can occur in the measurements. Data were taken in a temperature range between 40 and 350 K, and for many samples measurements were performed at several reduced temperatures, T/Tc. The first layer of Co on the Cu(100) surface shows an enhanced orbital moment, in contrast to the subsequent layers where the orbital moment is bulklike. The lowering of the symmetry, the enhanced spin moment, and the increased value of the density of states at the Fermi level are factors that combine to give the observed enhancements. © 1996 American Institute of Physics. [S0021-8979(96)679608-0]
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 5587-5591 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Over the past decade, we have: (1) developed phenomenological theory for the behavior of "well-ordered'' magnetic states of moderately delocalized light rare-earth and actinide systems (characteristically obtaining unusual anisotropic magnetism in agreement with experiment); (2) developed theory and computational technique to synthesize first principles electronic structure information into that phenomenological theory to make it materially predictive. As discussed in this paper, the resulting theory allows us to predict the triggering of an instability from unusual anisotropic, but well-ordered, magnetism to an unstable state. The unstable state can be either of a valence fluctuation type or of what probably is a heavy fermion type, and the detailed way in which these two types of instability is triggered differs.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 3683-3685 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A sharp change in the nature of the magnetic ordering has been observed on going from CeSb to CeTe, both of which have NaC1 structures with a small decrease in lattice parameter. This is an interesting example of the way in which hybridization of partially delocalized f electrons with band electrons gives rise to highly unusual magnetic properties which show great chemical sensitivity. In the present paper we apply our previous ab initio treatment of hybridization-induced effects to investigate this striking change in magnetic behavior. We have performed self-consistent warped muffin-tin LMTO band calculations treating the Ce 4f states as resonance states that are constrained to be localized. Compared to CeSb, the anion-derived p bands in CeTe sink well below the Fermi energy, thus strongly changing the band-f hybridization. We have calculated the hybridization dressing of the crystal-field levels and the anisotropic two-ion exchange interaction and compared them with those calculated for CeSb and with experiment. A strong decrease in the two-ion interaction explains the drastic change in observed magnetic behavior between CeSb and CeTe.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 3185-3187 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The unusual magnetic ordering, magnetic excitation behavior, and anomalous crystal-field splitting in CeBi and CeSb can be explained using a model Hamiltonian obtained by applying the Schrieffer–Wolff transformation to the Anderson Hamiltonian. It is highly desirable to obtain a first principles prediction of the parameters of the theory in order to extend this understanding quantitatively to other cerium and light actinide materials. To this end, we have calculated the electronic structure of CeBi and CeSb with the linear muffin-tin orbital (LMTO) method, using a self-consistent fully warped potential, and have obtained the coupling between non-f band states and f states localized in the sense of the Anderson Hamiltonian. This is applied to a calculation of the anomalous crystal-field splitting in CeBi and CeSb, and application to calculating the anisotropic two-ion interaction is discussed. We find that the dominant contribution to the anomalous crystal-field effect (about two thirds) comes from hybridization with d bands.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 374 (1995), S. 524-525 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] THE crystal structures of the light actinides have intrigued physicists and chemists for several decades1. Simple metals and transition metals have close-packed, high-symmetry structures, such as body-centred cubic, face-centred cubic and hexagonal close packing. ...
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Following the discovery of stishovite (the highest-pressure polymorph of silica known from natural samples), many attempts have been made to investigate the possible existence of denser phases of silica at higher pressures. Based on the crystal structures observed in chemical analogues of ...
    Type of Medium: Electronic Resource
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