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Mark Bailey
Materials Science Division
Appointment: 06/2005 - 02/2007
Supervisors: Kenneth Gray and
John Mitchell
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General Information
- Head of Materials Synthesis
- Wildcat Discovery Technologies, Inc.
- 6985 Flanders Drive
- San Diego, CA 92121
- Phone: (858) 550-1986 (direct)
- Fax: (858) 638-7533 (fax)
- Email: mbailey@wildcatdiscovery.com
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ANL Research Highlights
1. Colossal Magnetoresistance
Single crystals of layered manganites have been grown with the easy-magnetization-axis along the c-axis, as well as perpendicular to this axis. For the c-axis-orientated samples a state of antiferromagnetically coupled ferromagnetic layers was found at low temperature where the material is nominally "metallic." Measuring the anisotropic conductance in the layered colossal magnetoresistance (CMR) manganites was shown to be strongly affected by the location of current and voltage terminals. At least six terminals are required to obtain reliable values, while unusual artifacts can appear using traditional four-terminal measurements. The anisotropic conductance of the layered CMR manganites is shown to go as the square of the zero-field magnetization (from neutron scattering) over a broad temperature range below Tc. This result contradicts the simple double-exchange model and needs explanation. Single crystals of La-Sr-Mn-O perovskite were grown to study the re-entrant Jahn-Teller distortion induced by onset of ferromagnetism. Sintered pellets of (La, Ca)MnO3 perovskite were grown, and it was found that the low-temperature transport is well fit by variable-range hopping plus a field-dependent channel of free carriers.
2. Superconductivity
Spectacular crystals of Bi2Sr2CaCu2Ox achieved the highest reported Tc of 95 K and improved metal-ion homogeneity, in particular the lack of antisite defects. The first evidence for coherent Josephson vortex flow for fields parallel to the Cu-O planes in these Bi2Sr2CaCu2Ox single crystals has been obtained. Point-contact tunneling into oxygen doped and depleted single crystals of Bi2Sr2CaCu2Ox has strongly suggested that the 'pseudogap' has superconductivity as its origin.
3. Reacted Surface Layers
Transient phase formation was monitored during early-stage oxidation of FeCrAl alloys using a variety of spectroscopic techniques. Ruby fluorescence was used to investigate compressive strains, growth strains and substrate creep, which play a central role in scale failure. In-plane and out-of-plane strains were found from an elastic analysis of the fluorescence data. Both strains were confirmed by x-ray diffraction. Local strain concentrations and relaxation were studied to investigate the role of surface irregularities. Large strain variations were observed across wavy interfaces and strain relaxation was observed up to 20 microns from edges and corners.
New Endeavors
I am currently heading up the Materials Division of Wildcat Discovery Technologies, a new startup company based in San Diego . We are interested in developing techniques for synthesizing new hydrogen storage materials.
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