Author's School

Graduate School of Arts & Sciences

Author's Department/Program

Physics

Language

English (en)

Date of Award

Summer 9-1-2014

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Chair and Committee

Stuart A Solin

Abstract

PART I: Investigation and Optimization of Extraordinary Electroconductance (EEC) Sensors

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.

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/cm2 irradiance of HeNe laser light and maximum a specific detectivity of D* = 3.67x1011 cmHz1/2/W.

PART II: The Role of Magnetic Disorder in the Formation of Spin Glasses

This thesis presents data on the magnetic properties of two classes of layered spin S=1/2 antiferromagnetic quasi-triangular lattice materials: Cu2(1-x)Zn2x(OH)3NO3 (0≤x≤0.65) and its long organic chain intercalated derivatives Cu2(1-x)Zn2x(OH)3C7H15COO.mH2O (0≤x≤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.

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.

Comments

This work is not available online per the author’s request. For access information, please contact digital@wumail.wustl.edu or visit http://digital.wustl.edu/publish/etd-search.html.

Permanent URL: http://dx.doi.org/10.7936/K74B2ZDN

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