Zin Tun

Convenient off-line error quantification and characterization of concentricity of two circles of rotation for diffractometer alignment

To ensure concentricity of the θ–2θ rotation stages, but with a very limited 2θ range of rotation, an alignment technique using two dial gauges mounted at right angles to each other (X and Y axes) is described. The deflections of the orthogonal dial gauges are measured as a function of 2θ, with their probes impinging on a cylindrical pin centred on the θ axis. The X and Y corrections required to bring the two rotation stages into concentricity can then be found using a least-squares fitting via a freestanding program or via the `solver optimization within the Microsoft Excel spreadsheet software. The same dial gauges provide guidance for applying the required positional corrections. An Excel spreadsheet for determining the X and Y corrections via least squares has been deposited.

Neutron scattering studies of geometrically frustrated pyrochlore antiferromagnets

Abstract Elastic and inelastic neutron scattering work on the cubic pyrochlore antiferromagnets Y2Mo2O7, Tb2Ti2O7, and Tb2Mo2O7 is reviewed. These materials are characterized by antiferromagnetically coupled moments residing on a network of corner-sharing tetrahedra. Geometrical frustration manifests itself strongly in such systems in that two of them display a spin-glass-like transition in the apparent absence of chemical disorder, while the other remains paramagnetic to at least 0.1 K, despite developing antiferromagnetic short-range order at 50 K.

Patterson analysis for layer profile determination by neutron or X‐ray reflectometry

The possibility of using Patterson analysis to interpret neutron or X-ray reflectometry data has been critically examined in terms of a hypothetical case study. The technique yields a highly accurate layer profile model provided the data are measured with a beam geometry that gives rise to unit reflectivity at Q = 0 only, i.e. Qc = 0. For those cases where a plateau of unit reflectivity extends out to finite Q, i.e. Qc > 0, a distorted model is obtained. A strategy to significantly improve this initial estimate of the model is proposed and demonstrated.

Experimental verification of the significance of trigonal coupling for the 14 lock-in in holmium

Abstract In the region between 20 and 132 K, holmium is in a spiral anti-ferromagnetic phase, with the wave vector, τ, of the spiral increasing from 0.16 to 0.28 reciprocal lattice units. Near simple values of τ (such as 1 4 , which occurs near 100 K), a magnetic field can cause a “lock-in”, where the variation of τ with temperature is arrested over a small temperature range. Recently, Jensen [Phys. Rev. B 54 (1996) 4021] predicted that the temperature width of this lock-in should be very strongly dependent on the magnetic field orientation in the plane containing the c- and b-axis. We have used the N5 triple-axis spectrometer at the NRU reactor, Chalk River, to measure the temperature width of the τ = 1 4 lock-in in holmium as a function of the orientation of a 2.6 T magnetic field applied in the (c–b) plane: Our results are substantially in agreement with Jensens prediction.