Low-Dimensional Quantum Antiferromagnets

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9302065 Reich A series of experiments are proposed to explore the ground state properties and excitations of low-dimensional antiferromagnetic materials that exhibit novel cooperative quantum effects. A zero- temperature phase transition will be explored by varying the parameters in the Hamiltonian of spin-1 chain through the application of pressure. A field-induced incommensurate soft mode in the spin-1/2 chain will be studied in detail. The properties of quantum systems with competing interactions will be examined through experiments on one-dimensional chains with next-nearest neighbor infractions and two-dimensional systems with geometrical frustration. The research will involve crystal growth and characterization, low-temperature thermodynamic measurements, and detailed studies of dynamical properties via inelastic neutron scattering. %%% This research involves the growth and characterization of materials which have magnetic properties largely constrained to occur along one- or two-dimensions. The magnetic properties become pronounced at low temperatures, and are also influenced by application of hydrostatic pressure. The research will provide fundamental information relevant to magnetism, and to the field of high-Tc superconducting materials. The materials will be investigated using magnetic measurements and by the technique of neutron scattering which reflects dynamical aspects of the atomic magnets in the various materials. ***