2,565 research outputs found
The trimer-based spin liquid candidate Ba4NbIr3O12
Ba4NbIr3O12, a previously unreported material with a triangular planar
geometry of Ir3O12 trimers, is described. Magnetic susceptibility measurements
show no magnetic ordering down to 1.8 K despite the Curie-Weiss temperature of
-13 K. The material has a very low effective magnetic moment of 0.80
{\mu}B/f.u. To look at the lower temperature behavior, the specific heat (Cp)
was measured down to 0.35 K; it shows no indication of magnetic ordering and
fitting a power law to Cp vs. T below 2 K yields the power {\alpha} = 3/4.
Comparison to the previously unreported trimer compound made with the 4d
element Rh in place of the 5d element Ir, Ba4NbRh3O12, is presented. The
analysis suggests that Ba4NbIr3O12 is a candidate spin liquid material.Comment: 19 pages, 7 main figures, 2 SI figure
A single crystal high-temperature pyrochlore antiferromagnet
We report the magnetic characterization of the frustrated transition metal
pyrochlore NaCaCoF. This material has high spin Co in CoF
octahedra in a pyrochlore lattice, and disordered non-magnetic Na and Ca on the
large-atom sites in the structure. Large crystals grown by the floating zone
method were studied. The magnetic susceptibility is isotropic, the Co moment is
larger than the spin-only value, and in spite of the large Curie Weiss theta
(-140 K), freezing of the spin system, as characterized by peaks in the ac and
dc susceptibility and specific heat, does not occur until around 2.4 K. This
yields a frustration index of f = / 56, an
indication that the system is highly frustrated. The observed entropy loss at
the freezing transition is low, indicating that magnetic entropy remains
present in the system at 0.6 K. The compound may be the realization of a
frustrated pyrochlore antiferromagnet with weak bond disorder. The high
magnetic interaction strength, strong frustration, and the availability of
large single crystals makes NaCaCoF an interesting alternative to rare
earth oxide pyrochlores for the study of geometric magnetic frustration in
pyrochlore lattices.Comment: Submitted to PRL; 14 pages, 4 figures, 2 table
Superconductivity in WO2.6F0.4 synthesized by reaction of WO3 with Teflon
WO3-xFx (x < 0.45) perovskite-like oxyfluorides were prepared by a chemically
reducing fluorination route using the polymer polytetrafluoroethylene (Teflon).
The symmetry of the crystal structures of WO3-xFx changes from monoclinic to
tetragonal to cubic as the fluorine content increases. Fluorine doping changes
insulating WO3 to a metallic conductor, and superconductivity (Tc = 0.4 K) was
discovered in the samples with fluorine contents of 0.41 < x < 0.45. This easy
fluorination method may be applicable to other systems and presents an
opportunity for finding new oxyfluoride superconductors.Comment: 9 pages, 3 figures, 2 tables. To be published in Phys Rev
The Reactivity of MgB2 with Common Substrate and Electronic Materials
The reactivity of MgB2 with powdered forms of common substrate and electronic
materials is reported. Reaction temperatures between 600 C and 800 C,
encompassing the range commonly employed in thin-film fabrication, were
studied. The materials tested for reactivity were ZrO2, yttria stabilized
zirconia (YSZ), MgO, Al2O3, SiO2, SrTiO3, TiN, TaN, AlN, Si, and SiC. At 600 C,
MgB2 reacted only with SiO2 and Si. At 800 C, however, reactions were observed
for MgB2 with Al2O3, SiO2, Si, SiC, and SrTiO3. The Tc of MgB2 decreased in the
reactions with SiC and Al2O3.Comment: 5 figure
The emergence of superconductivity in BaNi2(Ge1-xPx)2 at a structural instability
The physical properties and structural evolution of the 122-type solid
solution BaNi2(Ge1-xPx)2 are reported. The in-plane X-X (X = Ge1-xPx) dimer
formation present in the end member BaNi2Ge2, which results in a structural
transition to orthorhombic symmetry, is completely suppressed to zero
temperature on P substitution near x = 0.7, and a dome-shape superconducting
phase with a maximum Tc = 2.9 K emerges. Clear indications of phonon softening
and enhanced electron-phonon coupling are observed at the composition of the
structural instability. Our findings show that dimer breaking offers new
possibilities as a tuning parameter of superconductivity.Comment: 14 pages, 4 figure
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