Rebecca J. Christianson

Critical dynamics of a spin-5/2 two-dimensional isotropic antiferromagnet

We report a neutron scattering study of the dynamic spin correlations in Rb

X-ray scattering and magnetic susceptibility study of doped CuGeO3

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SPIN CORRELATIONS IN AN ISOTROPIC SPIN-5/2 TWO-DIMENSIONAL ANTIFERROMAGNET

MnF

X-ray Scattering Studies of Two Length Scales in the Critical Fluctuations of CuGeO3

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Structures and Incommensurate Spin Excitations in Excess Oxygen-Doped La2CuO4+y

, a two-dimensional spin-5/2 antiferromagnet. By tuning an external magnetic field to the value for the spin-flop line, we reduce the effective spin anisotropy to essentially zero, thereby obtaining a nearly ideal two-dimensional isotropic antiferromagnet. From the shape of the quasielastic peak as a function of temperature, we demonstrate dynamic scaling for this system and find a value for the dynamical exponent

Structural Phase Transitions and Incommensurate Spin Fluctuations in the La2CuO4+y System

z

Incommensurate Spin Fluctuations in High-Transition Temperature Superconductors

. We compare these results to theoretical predictions for the dynamic behavior of the two-dimensional Heisenberg model, in which deviations from

Time-dependent strength of colloidal gels.

z=1

Limits to Gelation in Colloidal Aggregation

provide a measure of the corrections to scaling.

Electrochemistry and Staging in La2CuO4+d

We report comprehensive synchrotron x-ray scattering and magnetic susceptibility studies of the doped spin–Peierls materials Cu 1- x Zn x GeO 3 and CuGe 1- y Si y O 3 . Temperature versus dopant concentration phase diagrams are mapped out for both Zn and Si dopants. The phase diagrams of both Cu 1- x Zn x GeO 3 and CuGe 1- y Si y O 3 closely resemble that of Cu 1- x Mg x GeO 3 , including the observation that the spin gap is established at a much higher temperature than the temperature at which the spin–Peierls dimerization attains long-range order. The spin–Peierls transitions in doped samples exhibit unusual phase transition behavior, characterized by highly rounded phase transitions, Lorentzian squared lineshapes, and very long relaxation times. Phenomenological explanations for these observations are given by considering the effects of competing random bond interactions as well as random fields generated by the dopants. We have also confirmed the reentrance of the spin–Peierls phase when the temperatu...