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Title:Studies of the static magnetic susceptibility and microwave properties of tetrathiofulvalinium-tetracyanoquinodimethane
Author(s):Herman, Ray Michael
Doctoral Committee Chair(s):Salamon, Myron B.
Department / Program:Physics
static magnetic susceptibility
microwave properties
Faraday method
metal-to-insulator transformation
Abstract:The static magnetic susceptibility of Tetrathiofulvalinium-Tetracyanoquinodimethane (TTF-TCNQ) was measured using the Faraday method. Particular attention was paid to the region below 60 K in order to investigate the metal-to-insulator transformation this material undergoes. Anomalies in the susceptibility were apparent near 55 K and 38'K corresponding to phase transitions at these temperatures which are involved in the metal to insulator transformation process. Measurements done on aligned single crystals indicated that there is no temperature dependence in the anisotropy of the susceptibility and, therefore, that the insulating state in this material is not magnetically ordered. The electron spin susceptibility is derived from the measured total susceptibility. An extrapolation of the data between the 38 K and 55 K anomalies gives a finite spin susceptibility at zero temperature. This indicates a two-chain model in which one set of chains contributes a temperature-independent Pauli spin susceptibility between the two phase transitions. This model is discussed and used to explain the temperature dependence of the spin susceptibility. In this model the TTF and TCNQ chains act somewhat independently of each other. Above the 55 K transition both sets of chains are assumed to be metallic and a gap appears at the Fermi surface on only one set of chains at this transition. This leads to an exponential temperature dependence of the spin susceptibility of this set while the other set of chains remains metallic, and contributes a temperature independent Pauli spin susceptibility. Near 38 K the metallic set of chains develops a gap at the Fermi surface,causing a further exponential reduction in the susceptibility. A temperature hysteresis of the 38 K anomaly indicates that this lower phase transition is of first order. Some indications of a very small anomaly near 47 K were observed, but this anomaly is not fully explained. Studies of the microwave properties of TTF-TCNQ are also presented. This work was done by deriving the microwave conductivity from electron spin resonance measurements and by attempting to obtain the conductivity and dielectric constant by sample perturbation of a degenerate bimodal cavity. Also discussed is a method of preparing TTF-TCNQ by a co-sublimation technique.
Issue Date:1976
Genre:Dissertation / Thesis
Rights Information:1976 Ray Michael Herman
Date Available in IDEALS:2011-07-05
Identifier in Online Catalog:2651685

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