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The study of randomness in tow-dimensional quantum antiferromagnets is at the forefront of research in the field of strongly correlated electron systems, yet there have been relatively few experimental model systems. Complementary neutron scattering and numerical experiments demonstrate that the spin-diluted Heisenberg antiferromagnet [La.sub.2][Cu.sub.1-z][(Zn,Mg).sub.z][O.sub.4] is an excellent model material for square-lattice site percolation in the extreme quantum limit of spin one-haft. Measurements of the ordered moment and spin correlations provide important quantitative information for tests of theories for this complex quantum-impurity problem., The field of low-dimensional quantum magnetism has been of enormous interest to the condensed-matter physics community ever since the discovery that [La.sub.2]Cu[O.sub.4], the parent compound of the original high-temperature superconductor [...]

Studies of the magnetic properties of cubic R(x)Y(1-x)Al(2) intermetallic random anisotropy magnets reveal that the magnetic anisotropy cooling below correlated spin glass or spin glass transition temperatures is uniaxial or unidirectional. High field magnetostriction data indicate a reduction in the Callen alpha exponent for the Tb series. Quasielastic neutron scattering data help evaluate the influence of temperatures on the magnetic correlation length of compounds in Dy series.

The x-ray diffraction (XRD) and neutron scattering techniques are used for examining the structural phase transformations of 0.7Pb(Mg(sub 1/3)Nb(sub 2/3))-0.3PbTiO3 (PMN-30percent PT). The structural transformation sequence of PMN-30percent PT is established as a function of temperature and electric field.

We revisit the phase diagram of the relaxor ferroelectric PMN-PT using neutron powder diffraction to test suggestions that residual oxygen vacancies and/or strain affect the ground state crystal structure. Powdered samples of PMN-PT were prepared with nominal compositions of, 0.20, 0.30, and 0.40 and divided into two identical sets, one of which was annealed in air to relieve grinding-induced strain and to promote an ideal oxygen stoichiometry. For a given composition and temperature the same structural phase is observed for each specimen. However, the distortions in all of the annealed samples are smaller than those in the as-prepared samples. Further, the diffraction patterns for, 0.20, and 0.30 are best refined using the monoclinicspace group. By comparing our neutron diffraction results to those obtained on single crystals having similar compositions, we conclude that the relaxor skin effect in PMN-PT vanishes on the Ti-rich side of the morphotropic phase boundary. [ABSTRACT FROM PUBLISHER]

Magnetism in a single crystal CaCu3Ti4O12 has been studied using elastic and inelastic neutron scattering. We have measured the order parameter of the antiferromagnetic phase transition at TN=24.1(1) K. The observed magnetic structure can be consistently described by spins ordered collinearly along the crystallographic [111] direction. A spin wave mode of ω=7.3(4) meV has been observed and compared with a linear spin wave theory. [Copyright &y& Elsevier]