Magnetic susceptibility of doped polyacetylene

Magnetic susceptibility measurements of ${[\mathrm{CH}{(\mathrm{As}{\mathrm{F}}_{5})}_{y}]}_{x}$ over the concentration range $0<~y<0.13$ 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 ${(\mathrm{CH})}_{x}$ are discussed, including the possibility of soliton-localized impurity states induced by charge transfer doping.

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