Title

Frustrated Magnetism In Distorted Triangular Lattice Materials; & Extraordinary Electroconductance In Iii-V Metal Semiconductor Hybrid Structures

Author

Jian Wu, Washington University in St. LouisFollow

Author's School

Graduate School of Arts & Sciences

Author's Department/Program

Physics

Language

English (en)

Date of Award

January 2010

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Chair and Committee

Stuart A Solin

Abstract

PART I: We have synthesized a series of spin S = 1/2 distorted triangular lattice materials Cu_2(1-x)Zn_2x(OH)₃NO₃and their long chain alkyl carboxylic group intercalated derivatives, Cu_2(1-x)Zn_2x(OH)₃(C₇H₁₅COO).mH₂O). Their structural properties, magnetic properties and specific heat have been carefully studied in this thesis. We found that antiferromagnetic-type long-range order develops in all the nitrate group compounds below the Neel temperatures T_N, which decreases with increasing Zn content. For the organic long chain intercalated samples, the temperature dependence of magnetic susceptibility suggests that the low temperature state is a spin-glass-like phase, or more specifically, a cluster glass. Typical glassy behaviors are also observed in the time evolution of the remanent magnetization data. The specific heat data displays no visible peaks, which agrees with many spin-glass-like materials. Moreover, we found that the susceptibility follows power laws with two different exponents a in two successive regimes above the freezing temperature T_f, from which we propose that quantum Griffiths phases could exist in the intermediate temperature regime. PART II: Extraordinary Electroconductance: EEC) belongs to a class of geometry driven interfacial effects EXX, where E = extraordinary and, to date, XX = magnetoresistance: MR), piezoconductance: PC) and optoconductance: OC). EEC is defined to be the percentage change in the device conductance with and without an external electric field. A well-designed EEC device can be used as a sensitive electric field sensor. In our study, a maximum 5.3% of EEC under an electric field of 2.5kV/cm at 300K has been obtained. The central part of our EEC devices is the vertical Au/Ti-GaAs metal-semiconductor Schottky interface. We found that the change in the sample conductance is due to the change in the depletion width under an external electric field. A two-layer analytical model was built to quantitatively explain the field dependence and geometrical dependence of the EEC effect. The predictions of this one adjustable parameter model agree very well the experimental results.

Comments

Permanent URL: http://dx.doi.org/10.7936/K72N50C7

Recommended Citation

Wu, Jian, "Frustrated Magnetism In Distorted Triangular Lattice Materials; & Extraordinary Electroconductance In Iii-V Metal Semiconductor Hybrid Structures" (2010). All Theses and Dissertations (ETDs). 384.
https://openscholarship.wustl.edu/etd/384