135 research outputs found
Room-temperature structural phase transition in the quasi-2D spin-1/2 Heisenberg antiferromagnet Cu(pz)(ClO)
Cu(pz)(ClO) (with pz denoting pyrazine CHN) is a
two-dimensional spin-1/2 square-lattice antiferromagnet with =
4.24 K. Due to a persisting focus on the low-temperature magnetic properties,
its room-temperature structural and physical properties caught no attention up
to now. Here we report a study of the structural features of
Cu(pz)(ClO) in the paramagnetic phase, up to 330 K. By employing
magnetization, specific heat, Cl nuclear magnetic resonance, and neutron
diffraction measurements, we provide evidence of a second-order phase
transition at = 294 K, not reported before. The absence of a
magnetic ordering across in the magnetization data, yet the
presence of a sizable anomaly in the specific heat, suggest a structural
order-to-disorder type transition. NMR and neutron-diffraction data corroborate
our conjecture, by revealing subtle angular distortions of the pyrazine rings
and of ClO counteranion tetrahedra, shown to adopt a configuration of
higher symmetry above the transition temperature.Comment: 10 pages, 12 figure
Low temperature crystal structure and local magnetometry for the geometrically frustrated pyrochlore Tb2Ti2O7
We report synchrotron radiation diffraction and muon spin rotation (muSR)
measurements on the frustrated pyrochlore magnet Tb2Ti2O7. The powder
diffraction study of a crushed crystal fragment does not reveal any structural
change down to 4 K. The muSR measurements performed at 20 mK on a mosaic of
single crystals with an external magnetic field applied along a three-fold axis
are consistent with published a.c. magnetic-susceptibility measurements at 16
mK. While an inflection point could be present around an internal field
intensity slightly above 0.3 T, the data barely support the presence of a
magnetization plateau.Comment: To appear in the proceedings of the 13th International Conference on
Muon Spin Rotation, Relaxation and Resonance, Grindelwald, Switzerland, 1-6
June 201
Sc2Ga2CuO7: A possible quantum spin liquid near the percolation threshold
Sc2Ga2CuO7 (SGCO) crystallizes in a hexagonal structure (space group: P63/mmc), which can be seen as an alternating
stacking of single and double triangular layers. Combining neutron, x-ray, and resonant x-ray diffraction we establish that
the single triangular layers are mainly populated by non-magnetic Ga3+ ions (85% Ga and 15% Cu), while the bi-layers have comparable population of Cu2+ and Ga3+ ions (43% Cu and 57% Ga). Our susceptibility measurements in the temperature range 1.8 - 400 K give no indication of any spin-freezing or magnetic long-range order (LRO).We infer an effective paramagnetic moment μeff = 1.79±0.09 μB and a Curie-Weiss temperature �CW of about −44 K, suggesting antiferromagnetic interactions between the Cu2+(S = 1/2) ions. Low-temperature neutron powder diffraction data showed no evidence for LRO down to 1.5
K. In our specific heat data as well, no anomalies were found down to 0.35 K, in the field range 0-140 kOe. The magnetic
specific heat, Cm, exhibits a broad maximum at around 2.5 K followed by a nearly power law Cm/ T� behavior at lower
temperatures, with � increasing from 0.3 to 1.9 as a function of field for fields upto 90 kOe and then remaining at 1.9 for fields
upto 140 kOe. Our results point to a disordered ground state in SGCO
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