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Interplay of Curie-type and Pauli-type magnetic susceptibilities in HCl-doped polyaniline pellets

The static magnetic susceptibility ($\chi$) of own-made HCl-doped polyaniline pellets is investigated experimentally over the full range of the protonation level $Y$ and in the temperature ($T$) range 10-300 K. The obtained results suggest that $\chi$ and the electrical conductivity $\sigma$ - which is known from previous work - are interrelated. Namely, there is a weakly $Y$ dependent crossover temperature $T^*$ where both $\chi$ and $\sigma$ undergo notable changes. In $\chi$, this refers to a simultaneous enhancement (reduction) of the Pauli-type susceptibility $\chi_{; ; ; \mathrm{; ; ; P}; ; ; }; ; ; $ and reduction (enhancement) of the Curie constant $C$ at $T=T^*$ when $T$ increases (decreases). Below $T<T^*$, where thermal effects are weak to moderate, a steep increase of $\chi_{; ; ; \mathrm{; ; ; P}; ; ; }; ; ; (Y)$ around $Y=0.3$ occurs together with a drop of $C(Y)$. The above findings are consistent with a picture in which, at $T^*$, spins that disappear from $C$ reappear in $\chi_{; ; ; \mathrm{; ; ; P}; ; ; }; ; ; $, and vice versa. This model is used to address the longitudinal and transversal electron localisation lengths as functions of $Y$, the former being estimated to take values in the range $7-8$ \AA $ $ and the latter in the range $1-2$ \AA.

conducting polymers; polyaniline; static magnetisation; magnetic susceptibility

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