The effect of doping on the spin-Peierls (SP) transition in single crystals of CuGehas been investigated using neutron scanering techniques and susceptibility measurements. When the Cuz+ site is partly substituted by either ZnZ+ (4%) or Nilt (1.5%) the SP is suppressed. and a long-range N&l state develops below TN = 2.8 K (a) and T,, = 2.2 K (Ni) with a wave vector of (0.1, I). This observation contrasts with earlier reports of a spin glass m s i d o n in the doped compounds in the same temperature range. Our results also indicate that the reported N&l state in the nominally pure compound results from impurities. Preliminary mea~urements of the Zn-doped sample show that the gap that opens in the magnetic excitations below Tsp collapses in the doped compound.
The beamline, which is situated on a bending magnet at ESRF, comprises a unique combination of instrumentation for high-resolution and magnetic single-crystal diffraction. White-beam operation is possible, as well as focused and unfocused monochromatic modes. In addition to an eleven-axis Huber diffractometer, which facilitates simple operation in both vertical and horizontal scattering geometries, there is an in-vacuum polarization analyser and slit system, mirrors for harmonic rejection, sub 4.2 K and 1 Tesla magnetic field sample environment, plus a diamond phase plate for polarization conditioning. The instrumentation developed specifically for this beamline is described, and its use illustrated by recent scientific results.
Rare earth titanate pyrochlores are known to exhibit magnetic frustration. Large, high quality single crystals of a series of oxide pyrochlores, R 2 Ti 2 O 7 , have been grown by the floating zone technique, using an infrared image furnace. The crystals are roughly 5-6 mm in diameter and 40-60 mm in length and have been grown for R = Pr, Nd, Sm, Tb, Dy, Ho, Er and Y. The crystals have been characterized and tested for their quality.
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