271 research outputs found
Thermodynamic properties of quadrupolar states in the frustrated pyrochlore magnet TbTiO
The low-temperature thermodynamic properties of the frustrated pyrochlore
TbTiO have been studied using the single crystal of
sitting in a long range ordered phase in the - phase diagram.
We observed that the specific heat exhibits a minimum around 2 K and slightly
increases on cooling, similar to a Schottky-like anomaly for canonical spin
ices. A clear specific-heat peak observed at K is ascribable
to the phase transition to a quadrupolar state, which contributes to a
relatively large change in entropy, J Kmol.
However, it is still smaller than for the ground state doublet of the
Tb ions. The entropy release persists to higher temperatures, suggesting strong
fluctuations associated with spin ice correlations above . We
discuss the field dependence of the entropy change for and
.Comment: 6 pages, 2 figure
Multiple superconducting transitions in the Sr3Ru2O7 region of Sr3Ru2O7-Sr2RuO4 eutectic crystals
We report superconducting properties of Sr3Ru2O7-Sr2RuO4 eutectic crystals,
consisting of the spin-triplet superconductor Sr2RuO4 with a monolayer stacking
of RuO2 planes and the metamagnetic normal metal Sr3Ru2O7 with a bilayer
stacking. Although Sr3Ru2O7 has not been reported to exhibit superconductivity
so far, our AC susceptibility measurements revealed multiple superconducting
transitions occurring in the Sr3Ru2O7 region of the eutectic crystals. The
diamagnetic shielding essentially reached the full fraction at low AC fields
parallel to the c axis. However, both the shielding fraction and the onset
temperature are easily suppressed by AC fields of larger than 0.1 mT-rms and no
anomaly was observed in the specific heat. Moreover, the critical field curves
of these transitions have a positive curvature near zero fields, which is
different from the upper critical field curve of the bulk Sr2RuO4. These facts
suggest that the superconductivity observed in the Sr3Ru2O7 region is not a
bulk property. To explain these experimental results, we propose the scenario
that stacking RuO2 planes, the building block of superconducting Sr2RuO4, are
contained in the Sr3Ru2O7 region as stacking faults.Comment: 8 pages, 10 figures, accepted for publication in Phys. Rev.
Superconductivity in Sr2RuO4-Sr3Ru2O7 eutectic crystals
Superconducting behavior has been observed in the Sr2RuO4-Sr3Ru2O7 eutectic
system as grown by the flux-feeding floating zone technique. A supercurrent
flows across a single interface between Sr2RuO4 and Sr3Ru2O7 areas at distances
that are far beyond those expected in a conventional proximity scenario. The
current-voltage characteristics within the Sr3Ru2O7 macrodomain, as extracted
from the eutectic, exhibit signatures of superconductivity in the bilayered
ruthenate. Detailed microstructural, morphological and compositional analyses
address issues on the concentration and the size of Sr2RuO4 inclusions within
the Sr3Ru2O7 matrix. We speculate on the possibility of inhomogeneous
superconductivity in the eutectic Sr3Ru2O7 and exotic pairing induced by the
Sr2RuO4 inclusions.Comment: Pages 4, figures 3, submitted to Phys. Rev. Let
Quadrupole order in the frustrated pyrochlore magnet Tb2Ti2O7
TMU International Symposium on "New Quantum Phases Emerging from Novel Crystal Structure" 24–25 September 2015, Tokyo, Japan.We have studied the hidden long-range order (LRO) of the frustrated pyrochlore magnet Tb2Ti2O7 by means of specific-heat experiments and Monte-Carlo (MC) simulations, which has been discussed as the LRO of quadrupole moments inherent to the non-Kramers ion of Tb3+. We have found that the sharp specific-heat peak is collapsed into a broad hump by magnetic fields above 0.3 T for H//[001]. This result, qualitatively reproduced by MC simulations, suggests that a field-induced magnetic state overcomes the quadrupolar LRO state, as a similar case of a classical spin ice. The present results support the interpretation that Tb2+xTi2-xO7+y is a unique material in the boundary between the quadrupolar (x >= x(c) = -0.0025) and spin-liquid (x <= x(c)) states, where the magnetic field along the [001] axis is a tuning parameter which induces the magnetic ordered state
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