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  • 1
    Electronic Resource
    Electronic Resource
    Hybridization-induced magnetism in correlated cerium systems : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6420-6422 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: There is a great change in the nature of the magnetic ordering on going from CeIn3, a local moment antiferromagnetic system, to CePb3, a heavy fermion itinerant antiferromagnetic system, both of which have Cu3Au crystal structure. We have applied ab initio electronic structure calculations, based on the linear-muffin-tin-orbital method, and a phenomenological theory of orbitally driven magnetic ordering, to study the effects of the band-f hybridization-induced interactions and the band-f exchange-induced interactions, pertinent to the magnetic behavior of these systems. The position of the Ce 4f energy level relative to the Fermi energy and the intra-atomic Coulomb interaction are obtained from a sequence of three total-energy supercell calculations with two, one and zero f electrons in the Ce 4f core. The calculations elucidate the origins in the electronic structure of the variation of the f-state resonance width characterizing the strength of the hybridization and the density of states at the Fermi energy characterizing the number and character of band states available for hybridization. We present results for the hybridization potential and the hybridization-induced exchange interactions on going from CeIn3 to CePb3, where the only obvious change is the addition of an anion p electron. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361957
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  • 2
    Electronic Resource
    Electronic Resource
    Understanding the great range of magnetic ordering behavior in correlated f-electron systems : 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. 6226-6228 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic ordering behavior of correlated f-electron systems varies widely. With regard to the value of the ordered moments, there are systems of saturated moment (e.g., CeSb), of moment somewhat reduced from the saturated value (e.g., UTe), of very small moment (e.g., UPt3) and of no moment at all (e.g., CeCu2Si2). We show that such wide diversity in magnetic ordering is a manifestation of the competition between (1) hybridization and exchange interaction and (2) localization and itinerancy. By analyzing these effects, we develop a theory which organizes the diverse magnetic behavior into a unified picture describable through one model Hamiltonian. An important feature of this analysis is that we recognize and treat the effect of band-f Coulomb exchange simultaneously with that of band-f hybridization. Rather than adopting the standard analysis using the "Kondo resonance''–"Kondo compensation'' concept, the development of this theory offers a new approach to treat the correlated f-electron state. The present theory naturally leads to a nonmagnetic singlet "Kondo state'' which is one of the possible states, along with other magnetic states which the system could be in, when the conditions determining the state of the system favor that choice. The f orbital motions and spin-orbital coupling are given full consideration in the theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358288
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  • 3
    Electronic Resource
    Electronic Resource
    Prediction of pressure-induced changes in magnetic ordering of correlated-electron uranium systems (invited) : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 7035-7040 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experimentally, hydrostatic pressure experiments provide a very sensitive way to probe the development of magnetic ordering in correlated-electron systems. We have now developed and applied theory allowing us to understand and quantitatively predict the variation of ordering temperature with pressure in uranium-based correlated-electron materials on a wholly predictive calculated basis, i.e., without using any experimental data as input in the calculation. The theory physically captures the changes in the f spectral density distribution in space and time that are driven by pressure-induced increased band-f hybridization. As a test case, we have predicted behavior in good agreement with experiment for UTe where experimentally (Link et al.) Tc increases from 104 K to a maximum of 181 K at 7.5 GPa and then decreases to 156 K at 17.5 GPa. Our calculations: (1) using full-potential total-energy calculations match the experimental lattice parameter change with pressure within 2% and provide the decrease in average 5f-electron number; (2) extract information from the electronic structure calculation on the hybridization-induced changes and insert this into many-body theory to calculate the increase in two-ion coupling with pressure (from increased f spectral admixture into the bands) giving the initial increase in Tc; (3) calculate the decrease in ordering temperature (in terms of coupling) with decreased 5f number (localized spectral density) which gives the ultimate decrease in Tc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356718
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  • 4
    Electronic Resource
    Electronic Resource
    Trend of f-electron localization and itinerancy in rare-earth and light-actinide systems : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5409-5411 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An important characteristic of correlated f-electron systems is their dual nature of having both degrees of localization and itinerancy. Their magnetic behavior evolves with the amount of delocalization they have. Rare-earth monopnictides are on the localized side, with weak delocalization related to hybridization. Uranium monopnictides are on the itinerant side, but localization cannot be fully neglected. To explore the problem from both the localized and the itinerant sides, we have been developing techniques to calculate the evolving properties of f-electron systems on a first principle ab initio basis. This involves: electronic structure calculations; calculating band-f hybridization; calculating Coulomb exchange interaction; and calculating magnetic ordering. In this work, we applied these techniques to evaluate the evolution of f-electron behavior from heavy rare earths to light rare earths to actinides. We will discuss how the degree of localization of the f electrons affects their hybridization and Coulomb exchange interaction with non-f band electrons, and how this influences the two-ion exchange interaction and magnetic ordering. Our calculation is for XSb where X=Ce, Nd, Tb, Er, Yb, U and for CeTe and UTe.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353698
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  • 5
    Electronic Resource
    Electronic Resource
    Anisotropic magnetism in hybridizing uranium systems : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5424-5426 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.353703
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  • 6
    Electronic Resource
    Electronic Resource
    First principle evaluation of hybridization and exchange effects for magnetic ordering in correlated-electron uranium systems : The 5th Joint MMM−Intermag Conference (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 6083-6085 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Cerium and light actinide compounds show widely varied f-electron phenomena. The f-electron behavior in these systems ranges from well-localized to heavy-fermion-like or itinerant. Over a period of time we have been developing techniques to evaluate the fundamental interactions for correlated f-electron systems, such as band-f hybridization and band-f exchange, and trying to understand their properties and trends in the evolution of the properties between different isostructural cerium and light actinide compounds on the basis of absolute first principle calculations. Previous calculations are successful in explaining a variety of f-electron properties in cerium monopnictides and monochalcogenides. When going from localized f-electron cerium systems to more itinerant f-electron uranium systems, the hybridization between f- and non-f-conduction electrons is strongly enhanced by the self banding of the f states. We develop a scheme to evaluate the hybridization from the starting point that the f states are viewed as bands. We apply this scheme to uranium monopnictides and monochalcogenides to calculate their magnetic ordering.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350053
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  • 7
    Electronic Resource
    Electronic Resource
    Absolute evaluation of combined hybridization-induced and RKKY-induced two-ion interaction in correlated electron systems : 35th annual conference on magnetism and magnetic materials San Diego, California (USA) 29 Oct − 1 Nov 1990 (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 5472-5474 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Cerium and light actinide materials have unusual properties, including suppressed crystal-field splitting and highly anisotropic ordered magnetism, that can be understood on the basis of the Coulomb interaction between partially delocalized f electrons and the non-f-band electrons. In setting the absolute scale of interaction energy for materially predictive theory, it is crucial to take account of all consequences of the Coulomb interaction which contribute to the two-ion interaction. These include both the hybridization-induced effect (i.e., band-f mixing effects treated by a one-electron potential) and the RKKY-type effect (arising from the band-f exchange interaction) and the cross effect. The RKKY interaction, when treated fully, provides both isotropic and anisotropic contributions to the two-ion interaction. We found the anisotropic part is similar in its angular dependence and range dependence to the hybridization-induced effects. Therefore, the qualitative anisotropic nature of observable magnetic effects is quite similar to that caused by hybridization-induced effects by themselves, but the scale of energy is changed. Our results for CeBi and CeSb are in agreement with both the qualitative nature of the magnetic ordering and crystal-field dressing and with the absolute scale of energy as shown by the Néel temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347995
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  • 8
    Electronic Resource
    Electronic Resource
    Absolute evaluation of magnetic ordering in correlated f-electron systems (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5194-5196 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.344659
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  • 9
    Electronic Resource
    Electronic Resource
    Trends of hybridization in correlated electron magnetism (invited) (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 5587-5591 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.342290
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  • 10
    Electronic Resource
    Electronic Resource
    Correlated band magnetism of cerium and actinide materials : The 41st annual conference on magnetism and magnetic materials (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 3856-3858 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We discuss (1) the effects to be expected by the introduction into the electronic structure of locally-based two-electron correlations between the f electrons and bonding electrons of p and d atomic origin centered off-site as well as f-f correlations, (2) the expected observable consequences of these two-electron correlations, and (3) how to perform electronic structure calculations including the two-electron correlations. We first review certain general features of the physics associated with capturing the dual energetically localized-delocalized nature of the f electron spectral density; and review model calculations involving a single on-site f electron and a single ligand p/d electron of off-site parentage which lead to the possibility of a narrow singlet and triplet (magnetic) band picture explaining heavy fermion phenomenology. We then show that the same singlet/magnetic state picture arises when we include two-electron f-l and f-f correlations for actinides, which have atomic fn configurations with n〉1; and we describe a practical electronic structure scheme for real materials based on a sequence in which a conventional one-electron linearized combination of muffin-tin orbitals (LMTO) LDA+U calculation is followed by a calculation for the lattice with a helium like two-electron Hamiltonian at the f atom sites, i.e., two-electron atoms where initially for the core two electrons worth of charge are removed from the LMTO f-site atom. This procedure will reconstruct the LMTO bands to include two-electron texturing. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364732
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