X-ray and neutron scattering studies of the Rb₂MnF₄ and Cu₁₋õxMgx̳GeO₃ in an external magnetic field

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.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Physics.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2001

Author dc:creator

• Christianson, Rebecca J. (Rebecca Jean), 1973-

Advisor dc:contributor.advisor

• Robert J. Birgeneau.

• Physics.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/8286

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/8286