Studies of the static magnetic susceptibility and microwave properties of tetrathiofulvalinium-tetracyanoquinodimethane
Herman, Ray Michael
This item is only available for download by members of the University of Illinois community. Students, faculty, and staff at the U of I may log in with your NetID and password to view the item. If you are trying to access an Illinois-restricted dissertation or thesis, you can request a copy through your library's Inter-Library Loan office or purchase a copy directly from ProQuest.
Permalink
https://hdl.handle.net/2142/25645
Description
Title
Studies of the static magnetic susceptibility and microwave properties of tetrathiofulvalinium-tetracyanoquinodimethane
Author(s)
Herman, Ray Michael
Issue Date
1976
Doctoral Committee Chair(s)
Salamon, Myron B.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
tetrathiofulvalinium-tetracyanoquinodimethane
static magnetic susceptibility
microwave properties
Faraday method
metal-to-insulator transformation
Language
en
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.
Use this login method if you
don't
have an
@illinois.edu
email address.
(Oops, I do have one)
IDEALS migrated to a new platform on June 23, 2022. If you created
your account prior to this date, you will have to reset your password
using the forgot-password link below.
