X-ray and neutron scattering studies of the Rb₂MnF₄ and Cu₁âõxMgxÌ³GeO₃ in an external magnetic field
Author(s)Christianson, Rebecca J. (Rebecca Jean), 1973-
Massachusetts Institute of Technology. Dept. of Physics.
Robert J. Birgeneau.
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This thesis presents results of two scattering studies of low dimensional magnetic materials. The first is a neutron scattering study of Rb2MnF4, a nearly ideal two-dimensional square lattice Heisenberg antiferromagnet with S = 5/2. When this material is placed in a magnetic field on an extrapolation of the spin-flop phase boundary into the paramagnetic phase, Heisenberg critical behavior can be accessed to a much longer correlation length than had previously been achieved for a high-spin system. Comparison of our results with current theories indicate that the probed temperature region lies in a crossover region from classical to renormalized classical behavior. In addition, we show measurements of both the quasielastic and magnon dynamic behavior. The second part of this thesis presents extensive synchrotron x-ray scattering measurements of the high-field incommensurate phase in doped CuGeO3. Random-field behavior, including Lorentzian-squared lineshapes, the changing of a first order transition to second-order, and critical destruction of long-range order is observed in this continuous order parameter system.
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2001.In title on t.p., double-underscored "x" appears as subscript.Includes bibliographical references (p. 111-115).
DepartmentMassachusetts Institute of Technology. Dept. of Physics.
Massachusetts Institute of Technology