Magnetic susceptibility of doped polyacetylene

Magnetic susceptibility measurements of ${\left[\mathrm{CH}{\left(\mathrm{As}{\mathrm{F}}_5\right)}_y\right]}_x$ over the concentration range $0<~y<\mathrm{}0.13\mathrm{}$ and the temperature range 77-295 K are presented. Measurements were performed using both Faraday balance and Schumacher-Slichter magnetic resonance methods. Total susceptibilities were separated into three components: atomic core diamagnetism, local-moment Curie-law paramagnetism, and Pauli paramagnetism. From the onset of the Pauli term as a function of (As${\mathrm{F}}_5$) concentration, the critical dopant concentration for the semiconductormental transition is determined. The Fermi-surface density of states obtained from the Pauli term is analyzed in terms of various band-structure models. Alternate explanations of anomalously small Curie terms in lightly doped, semiconducting ${\left(\mathrm{CH}\right)}_x$ are discussed, including the possibility of soliton-localized impurity states induced by charge transfer doping.