96 research outputs found
Infrared evidence of a Slater metal-insulator transition in NaOsO3
The magnetically driven metal-insulator transition (MIT) was predicted by
Slater in the fifties. Here a long-range antiferromagnetic (AF) order can open
up a gap at the Brillouin electronic band boundary regardless of the Coulomb
repulsion magnitude. However, while many low-dimensional organic conductors
display evidence for an AF driven MIT, in three-dimensional (3D) systems the
Slater MIT still remains elusive. We employ terahertz and infrared spectroscopy
to investigate the MIT in the NaOsO3 3D antiferromagnet. From the optical
conductivity analysis we find evidence for a continuous opening of the energy
gap, whose temperature dependence can be well described in terms of a second
order phase transition. The comparison between the experimental Drude spectral
weight and the one calculated through Local Density Approximation (LDA) shows
that electronic correlations play a limited role in the MIT. All the
experimental evidence demonstrates that NaOsO3 is the first known 3D Slater
insulator.Comment: 4 figure
Magnetic and structural studies of Sc containing ruthenate double perovskites A2ScRuO6 (A = Ba, Sr).
Ruthenium containing double perovskites A2ScRuO6 have been synthesized as polycrystalline powders and structurally characterized using a combination of synchrotron X-ray and neutron powder diffraction methods. When A = Ba a hexagonal 6L perovskite structure is obtained if the synthesis is conducted at ambient pressure and a rock-salt ordered cubic structure obtained if the sample is quenched from high pressures. The Sr oxide Sr2ScRuO6 is obtained with a rock-salt ordered corner sharing topology. Heat capacity and bulk magnetic susceptibility measurements show the three oxides are antiferromagnets. Cubic Ba2ScRuO6 undergoes a metal-insulator transition near 270 K and hexagonal Ba2ScRuO6 is a semiconductor with an activation energy of 0.207 eV. The magnetic structures of the two rock-salt ordered double perovskites were established using powder neutron diffraction, and are described by k = (001) and k = (000) for the Ba and Sr oxides respectively, corresponding to type I antiferromagnetic structures, with ferromagnetic layers stacked antiferromagnetically. The ambient pressure hexagonal polymorph of Ba2ScRuO6 has partial Sc-Ru ordering at both the face-sharing B2O9 dimer and corner sharing BO6 sites. The magnetic structure is described by k = (½ 0 0) with the basis vector belonging to the irreducible representation Γ3.Australian Synchrotron Australian Research Counci
Evolution of the magnetic excitations in NaOsO through its metal-insulator transition
The temperature dependence of the excitation spectrum in NaOsO
through its metal-to-insulator transition (MIT) at 410 K has been investigated
using resonant inelastic X-ray scattering (RIXS) at the Os L edge.
High resolution ( 56 meV) measurements show that the
well-defined, low energy magnons in the insulating state weaken and dampen upon
approaching the metallic state. Concomitantly, a broad continuum of excitations
develops which is well described by the magnetic fluctuations of a nearly
antiferromagnetic Fermi liquid. By revealing the continuous evolution of the
magnetic quasiparticle spectrum as it changes its character from itinerant to
localized, our results provide unprecedented insight into the nature of the MIT
in NaOsO.Comment: Accepted in Physical Review Letters, part of a joint submission to
Physical Review B. Supersedes arXiv:1707.0555
Unusual effects of magnetic dilution in the ferrimagnetic columnar ordered perovskites
Powder neutron diffraction experiments have been employed to establish the
effects of site-selective magnetic dilution in the Sm2MnMnMn4-x Tix O12 A-site
columnar ordered quadruple perovskite manganites (x = 1, x = 2 and x = 3). We
show that in all three compositions the Mn ions adopt a collinear ferrimagnetic
structure below 27 K, 62 K and 34 K, respectively. An unexpected increase in
the ordering temperature was observed between the x = 1 and x = 2 samples,
which indicates a considerable departure from mean field behaviour. This result
is corroborated by large reductions in the theoretical ground state magnetic
moments observed across the series, which indicate the presence of spin
fluctuations and or disorder. We show that long range magnetic order in the x =
3 sample, which occurs below the percolation threshold for B-B exchange, can
only be understood to arise if magnetic order in Sm2MnMnMn4-xTixO12 is mediated
via both A-B and B-B exchange, hence confirming the importance of A-B exchange
interactions in these materials. Finally we show that site-selective magnetic
dilution enables the tuning of a ferrimagnetic compensation point and the
introduction of temperature-induced magnetization reversal.Comment: 10 pages, 7 figure
Superconductivity suppression of Ba0.5K0.5Fe2-2xM2xAs2 single crystals by substitution of transition-metal (M = Mn, Ru, Co, Ni, Cu, and Zn)
We investigated the doping effects of magnetic and nonmagnetic impurities on
the single-crystalline p-type Ba0.5K0.5Fe2-2xM2xAs2 (M = Mn, Ru, Co, Ni, Cu and
Zn) superconductors. The superconductivity indicates robustly against impurity
of Ru, while weakly against the impurities of Mn, Co, Ni, Cu, and Zn. However,
the present Tc suppression rate of both magnetic and nonmagnetic impurities
remains much lower than what was expected for the s\pm-wave model. The
temperature dependence of resistivity data is observed an obvious low-T upturn
for the crystals doped with high-level impurity, which is due to the occurrence
of localization. Thus, the relatively weak Tc suppression effect from Mn, Co,
Ni, Cu, and Zn are considered as a result of localization rather than
pair-breaking effect in s\pm-wave model.Comment: 8 pages, 9 figures, to be published in Phys. Rev.
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