982 research outputs found
Synthesis, Crystal Structure and Magnetic Properties of the Linear-Chain Cobalt Oxide Sr5Pb3CoO12
The novel spin-chain cobalt oxide Sr5Pb3CoO12 [P-62m, a = 10.1093(2) A and c
= 3.562 51(9) A at 295 K] is reported. Polycrystalline sample of the compound
was studied by neutron diffraction (at 6 and 295 K) and magnetic susceptibility
measurements (5 to 390 K). The cobalt oxide was found to be analogous to the
copper oxide Sr5Pb3CoO12, which is comprised of magnetic-linear chains at
inter-chain distance of 10 A. Although the cobalt oxide chains (mu_eff of 3.64
mu_B per Co) are substantially antiferromagnetic (theta_W = -38.8 K), neither
low-dimensional magnetism nor long-range ordering has been found; a
local-structure disorder in the chains might impact on the magnetism. This
compound is highly electrically insulating.Comment: To be published in J. Solid State Che
Metallic conductivity and a Ca substitution study of NaRh2O4 comprising a double chain system
The metallic compound NaRh2O4 forms a full range solid solution to the
insulating phase CaRh2O4. At a Na concentration of 0.25 moles per formula unit,
we found an unexpected contribution to the specific heat at low temperature [K.
Yamaura et al. Chem. Mater. 17 (2005) 359]. To address this issue, specific
heat and ac and dc magnetic susceptibilities were additionally measured under a
variety of conditions for the Na0.25 sample. A new set of data clearly indicate
the additional specific heat is magnetic in origin; however, the magnetic
entropy is fairly small (~1 % of Schottky term for a simple splitting doublet),
and there is no other evidence to suggest that a magnetic phase transition is
responsible for the anomalous specific heat.Comment: Accepted for publication in a special issue of Physica B (the
proceedings of SCES05
Magnetic studies of the lightly Ru doped perovskite rhodates Sr(Ru,Rh)O
The solid solution between the ferromagnetic metal SrRuO and the enhanced
paramagnetic metal SrRhO was recently reported [K. Yamaura et al., Phys.
Rev. B 69 (2004) 024410], and an unexpected feature was found in the specific
heat data at =0.9 of SrRuRhO. The feature was reinvestigated
further by characterizing additional samples with various Ru concentrations in
the vicinity of =0.9. Specific heat and magnetic susceptibility data
indicate that the feature reflects a peculiar magnetism of the doped
perovskite, which appears only in the very narrow composition range
0.850.95.Comment: Accepted for publication in a special issue of Physica B (the
proceedings of SCES04
Extremely strong-coupling superconductivity and anomalous lattice properties in the beta-pyrochlore oxide KOs2O6
Superconducting and normal-state properties of the beta-pyrochlore oxide
KOs2O6 are studied by means of thermodynamic and transport measurements. It is
shown that the superconductivity is of conventional s-wave type and lies in the
extremely strong-coupling regime. Specific heat and resistivity measurements
reveal that there are characteristic low-energy phonons that give rise to
unusual scattering of carriers due to strong electron-phonon interactions. The
entity of the low-energy phonons is ascribed to the heavy rattling of the K ion
confined in an oversized cage made of OsO6 octahedra. It is suggested that this
electron-rattler coupling mediates the Cooper pairing, resulting in the
extremely strong-coupling superconductivity.Comment: 17 pages (only 4 pages included here. go to
http://hiroi.issp.u-tokyo.ac.jp/Published%20papers/K-SC6.pdf for full pages),
to be published in PR
Electronic properties of the novel 4d metallic oxide SrRhO3
The novel 4d perovskite compound SrRhO3 was investigated by isovalent doping
studies. The solubility limits of Ca and Ba onto Sr-site were below 80% and
20%, respectively. Although SrRhO3 was chemically compressed, approximately
5.7% by the Ca doping, no significant influence was observed on the magnetic
and electrical properties.Comment: To be published in a special issue of Physica B (the proceedings of
LT23
Non-magnetic pair-breaking effect on La(Fe_{1-x}Zn_{x})AsO_{0.85} studied by NMR and NQR
As and La NMR and nuclear quadrupole resonance (NQR) studies
on Zn-substituted LaFeAsO have been performed to investigate the
Zn-impurity effects microscopically. Although superconductivity in
LaFeAsO disappears by 3% Zn substitution, we found that NMR/NQR
spectra and NMR physical quantities in the normal state are hardly changed,
indicating that the crystal structure and electronic states are not modified by
Zn substitution. Our results suggest that the suppression of superconductivity
by Zn substitution is not due to the change of the normal-state properties, but
due to strong non-magnetic pair-breaking effect to superconductivity.Comment: 5 pages, 4 figures, This paper was chosen as "Paper of Editors'
Suggestion
Magnetic phase transitions in SmCoAsO
Magnetization, x-ray diffraction and specific-heat measurements reveal that
SmCoAsO undergoes three magnetic phase transitions. A ferromagnetic transition
attributed to the Co ions, emerges at TC=57 K with a small saturation moment of
0.15muB/Co. Reorientation of the Co moment to an antiferromagnetic state is
obtained at TN2=45 K. The relative high paramagnetic effective moment Peff=1.57
MuB/Co indicates an itinerant ferromagnetic state of the Co sublattice. The
third magnetic transition at TN1=5 K is observed clearly in the specific-heat
study only. Both magnetic and 57Fe Mossbauer studies show that substitution of
small quantities of Fe for Co was unsuccessful.Comment: 10pages text+Figures: comments welcome ([email protected]
Effects of Rattling Phonons on the Quasiparticle Excitation and Dynamics in the Superconducting -Pyrochlore KOsO
Microwave penetration depth and surface resistance at 27 GHz are
measured in high quality crystals of KOsO. Firm evidence for
fully-gapped superconductivity is provided from . Below the second
transition at K, the superfluid density shows a step-like
change with a suppression of effective critical temperature .
Concurrently, the extracted quasiparticle scattering time shows a steep
enhancement, indicating a strong coupling between the anomalous rattling motion
of K ions and quasiparticles. The results imply that the rattling phonons help
to enhance superconductivity, and that K sites freeze to an ordered state with
long quasiparticle mean free path below .Comment: 5 pages, 5 figures, to be published in Phys. Rev. Let
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