57 research outputs found
Dynamical Mean Field Theory of the Antiferromagnetic Metal to Antiferromagnetic Insulator Transition
We study the antiferromagnetic metal to antiferromagnetic insulator using
dynamical mean field theory and exact diagonalization methods. We find two
qualitatively different behaviors depending on the degree of magnetic
correlations. For strong correlations combined with magnetic frustration, the
transition can be described in terms of a renormalized slater theory, with a
continuous gap closure driven by the magnetism but strongly renormalized by
correlations. For weak magnetic correlations, the transition is weakly first
order.Comment: 4 pages, uses epsfig,4 figures,notational errors rectifie
Magnetic Phase Diagram and Metal-Insulator Transition of NiS2-xSex
Magnetic phase diagram of NiS2-xSex has been reexamined by systematic studies
of electrical resistivity, uniform magnetic susceptibility and neutron
diffraction using single crystals grown by a chemical transport method. The
electrical resistivity and the uniform magnetic susceptibility exhibit the same
feature of temperature dependence over a wide Se concentration. A distinct
first order metal-insulator (M-I) transition accompanied by a volume change was
observed only in the antiferromagnetic ordered phase for 0.50<x<0.59. In this
region, the M-I transition makes substantial effects to the thermal evolution
of staggered moments. In the paramagnetic phase, the M-I transition becomes
broad; both the electrical resistivity and the uniform magnetic susceptibility
exhibit a broad maximum around the temperatures on the M-I transition-line
extrapolated to the paramagnetic phase.Comment: 6 pages, 8 figures, corrected EPS fil
Metal-insulator Crossover Behavior at the Surface of NiS_2
We have performed a detailed high-resolution electron spectroscopic
investigation of NiS and related Se-substituted compounds
NiSSe, which are known to be gapped insulators in the bulk at all
temperatures. A large spectral weight at the Fermi energy of the room
temperature spectrum, in conjunction with the extreme surface sensitivity of
the experimental probe, however, suggests that the surface layer is metallic at
300 K. Interestingly, the evolution of the spectral function with decreasing
temperature is characterized by a continuous depletion of the single-particle
spectral weight at the Fermi energy and the development of a gap-like structure
below a characteristic temperature, providing evidence for a metal-insulator
crossover behavior at the surfaces of NiS and of related compounds. These
results provide a consistent description of the unusual transport properties
observed in these systems.Comment: 12 pages, 3 figure
X-ray photoemission study of NiS_{2-x}Se_x (x = 0.0 - 1.2)
Electronic structure of NiS_{2-x}Se_x system has been investigated for
various compositions (x) using x-ray photoemission spectroscopy. An analysis of
the core level as well as the valence band spectra of NiS_2 in conjunction with
many-body cluster calculations provides a quantitative description of the
electronic structure of this compound. With increasing Se content, the on-site
Coulomb correlation strength (U) does not change, while the band width W of the
system increases, driving the system from a covalent insulating state to a
pd-metallic state.Comment: 19 pages, 6 figures, To appear in Phys. Rev. B, 200
II-3. Application of genomic database for the control of pathogenic diseases of cultured fish
MAGNETIC TORQUE STUDY OF MnCr2O4 AT LOW TEMPERATURES
On a mesuré l'anisotropie magnétique par mesures de couple
de 4,2 °K jusqu'a 45°K (= Tc). A 20 °K. K1 = — 4,l x
104 erg/cc. Une valeur négative de K1 ne peut s'expliquer
par un modèle d'anisotropie à un ion et par l'interaction des dipôles
magnétiques dans le cas d'un arrangement colinéaire des spins. Au-dessous de 18
°K, une hystérésis de rotation indépendante de l'intensité du champ magnétique
est observée. Une tentative d'explication du mécanisme de cette hystérésis est
proposée.Magnetic torque measurement from 4.2 °K to 45 °K (=
Tc) are described. At 20 °K, K1 = — 4.1 x 104
ergs/cc. Negative K1 can not be explained from single ion anisotropy
and dipolar interaction, provided that colinear spin arrangement is assumed.
Below 18 °K rotational hysteresis, independent of magnetic field intensity, was
observed. A tentative of mechanism of this rotational hysteresis is
given
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