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Notes: Abstract: 1-(n-decyl)-3-Pyrazolidinone (BW357U) is a potent, selective inhibitor of gamma-aminobutyrate aminotransferase (GABA-T) in vitro and in vivo. After acute or chronic, oral or intraperitoneal administration of BW357U to rats, brain GABA levels were elevated in a dose-dependent manner. When inhibition of brain GABA-T exceeded 50%, whole brain GABA levels were elevated approximately threefold, and an anorectic effect was observed in the absence of other symptoms. This compound, because of its potency and selectivity, may be useful in studies relating to the function of GABA-containing neurons in appetite regulation.

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.

Notes: We have applied the model and technique previously applied to the change of Curie temperature with pressure for correlated-electron uranium systems to predict the change in Curie temperature and ordered moment with dilution alloying. The theory is remarkably successful in its predictions, and this success has important implications for the overall understanding of magnetic ordering in correlated-electron systems including heavy fermion systems. For US, the dilution alloying behavior found experimentally is dramatic. In UxLa1−xS, the magnetic ordering abruptly disappears at about 55% uranium. Our ab initio-based theory quantitatively predicts this abrupt disappearance while also quantitatively predicting the monotonic decrease of Curie temperature with pressure for undiluted US. In addition, in agreement with experiment, the theory predicts the correct trend for the magnetic ordering to disappear with dilution, while at the same time absolutely and quantitatively predicting the nonmonotonic variation of Curie temperature with pressure, for USe and UTe. The ab initio-based model gives absolute material-specific predictions using input from the local density approximation paramagnetic uranium f-electron-projected density of states plus ab initio calculated values of the correlation energy U. The key physics of the model is the recognition and quantification of the concept that the f spectral density in the vicinity of a specific uranium nucleus (so-to-speak in the muffin-tin sphere) can either be in a stable f3 configuration for a long enough period of time that, through coupling to other such stable f3 sites, it can magnetically order, or can be in a situation such that the configuration fluctuates rapidly between f3 and f2, and for purposes of magnetic ordering acts like a hole in the f-electron lattice in the same way that substitution of lanthanum for uranium creates a hole. Both pressure and dilution alloying, by causing an increase in f-delocalization, increase the fraction of uranium sites in the rapidly fluctuating, magnetically ineffective, condition. For dilution alloying, at a certain point this increase in fluctuations causes the stable f3 component to fall abruptly below a critical value necessary to sustain any magnetic ordering, and hence brings about a catastrophic collapse in magnetic ordering. © 1998 American Institute of 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.

Notes: We have investigated how the behavior of a transition shell atomic species (species A) with orbital magnetism, driven by hybridization-mediated interactions via a sea of band electrons, is modified by the addition of a second parasite hybridizer (species B). Our approach involves a two-stage procedure. First, we calculate the modification of the band electron sea by hybridization with B by using a slave boson formalism. Second, the modifications in the A-A interionic interactions driving the orbital magnetic ordering are calculated by applying a Schrieffer–Wolff transformation on the renormalized Anderson lattice hamiltonian obtained from the first stage. The new A-A interactions have a different radial dependence (range factor) which depends in a nonlinear way on the band-B hybridization strength: and the consequences of this change on the magnetic ordering are studied using a mean-field approximation. This enables us to model the reduction in the magnetic ordering caused by competing parasite hybridization, and the dependence of this reduction on the relative hybridization strengths of the two species.

Notes: It is well known that CeSb displays the largest ferromagnetic Kerr rotation known with a peak value of over 14°, which is about 30 times that of the strongly magnetic material iron. Conventional magneto-optical theory for magnetically ordered materials ascribes the magneto-optic effects to spin-orbit coupling. We have suggested1 that in such highly correlated partially-delocalized f-electron systems where the magnetization is orbitally driven, the electromagnetic wave couples directly to the electronic magnetization. We believe that such a coupling avoids the weak linkage provided by spin-orbit coupling and is responsible for the giant magneto-optic rotation in CeSb. We first did a conventional itinerant electron (band magnetism) calculation to see if it gives the correct Kerr rotation. The band structure used is obtained from a self-consistent spin-polarized full-potential LMTO calculation with a true interstitial. As a test, we have also calculated the magneto-optic rotation in both bcc and fcc iron where the conventional theory provides good agreement with experiment.〈ks〉

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.

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.

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.

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.