Investigation and Optimization of Extraordinary Electroconductance (EEC) Sensors & The Role of Magnetic Disorder in the Formation of Spin Glasses

<p><underline>PART I: Investigation and Optimization of Extraordinary Electroconductance (EEC) Sensors</underline></p><p>This thesis presents an investigation and geometric optimization of Extraordinary Electroconductance (EEC) sensors, a member of an established class of sensors that exhibit `extraordinary' phenomenon driven by interfaces that maximize current redistribution under an applied perturbation. EEC sensors are responsive to both applied electrical fields and optical illumination and show promising application in the detection of complex biological signals that can aid in conclusive diagnoses.</p><p>The EEC device response to nonuniform illumination establishes greater versatility for EEC devices by allowing for position-dependent light sensing while under local illumination. Additionally, an enhanced light responsivity of EEC sensors via modification of shunt geometry, as well as a bifurcation in sensor response to direct reverse bias and light irradiance based on measurement lead location was observed. Significantly increased light responsivity was achieved by simultaneously biasing the EEC device while exposing to light, resulting in an over 614% increase in resistance from 11mW/cm<super>2</super> irradiance of HeNe laser light and maximum a specific detectivity of D* = 3.67x10<super>11</super> cmHz<super>1/2</super>/W.</p><p><underline>PART II: The Role of Magnetic Disorder in the Formation of Spin Glasses</underline></p><p>This thesis presents data on the magnetic properties of two classes of layered spin S=1/2 antiferromagnetic quasi-triangular lattice materials: Cu_2(1-x)Zn_2x(OH)₃NO₃ (0&le;x&le;0.65) and its long organic chain intercalated derivatives Cu_2(1-x)Zn_2x(OH)₃C₇H₁₅COO.mH₂O (0&le;x&le;0.29), where non-magnetic Zn substitutes for Cu isostructurally. It is found that the intercalated compounds, even in a clean system in the absence of dilution, x=0, show spin-glass behavior, as evidenced by DC and AC susceptibility measurements, and by time dependent magnetization measurements. A striking feature is the observation of a sharp crossover between two successive power law regimes in the DC susceptibility above the freezing temperature. In contrast to standard theoretical expectations, these power laws are insensitive to doping. Specific heat data are consistent with a conventional phase transition in the unintercalated compounds, and glassy behavior in the intercalated compounds.</p><p>The emergence of a cluster spin glass under no imposed magnetic disorder suggests that the historical assumption that magnetic disorder is required to form a spin glass may be wrong. Research into additional examples of non-diluted spin glasses should lend phenomenological insight into the factors driving the frustrated magnetic system into a spin glass phase.</p>

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Year dc:date.available

2014

Author dc:creator

• Werner, Fletcher M.

Contributors dc:contributor

• Stuart A Solin

• EEC
• extraordinary
• frustrated magnetism
• sensors
• spin glass

Language dc:language

English (en)

DOI

https://doi.org/10.7936/K74B2ZDN

OAI identifier oai:identifier

oai:openscholarship.wustl.edu:etd-2362