Antiferromagnetism in the organic conductor bis-tetramethyltetraselenafulvalene hexafluoroarsenate [${\mathrm{}\left(\mathrm{TMTSF}\right)\mathrm{}}_2$As${\mathrm{F}}_6$]: Static magnetic susceptibility

The anisotropy in the static magnetic susceptibility of bis-tetramethyltetraselenafulvalene hexafluoroarsenate [${\mathrm{}\left(\mathrm{TMTSF}\right)\mathrm{}}_2$As${\mathrm{F}}_6$] has been investigated above and below the metal-to-insulator transition for a range of fields between 0.5 and 30 kG. The results are consistent with the expectations of a simple antiferromagnet with easy, intermediate, and hard axes close to the crystallographic $b^{*}$, $a$, and $c^{*}$ directions. Below the transition temperature $T_c=12\mathrm{}$ K, a spin-flop transition is seen. The temperature dependence of the spin-flop critical field $H_c=4.5\mathrm{}$ kG is insignificant. Above the transition temperature, evidence for magnetic crossover is observed. The experimental results show ${\mathrm{}\left(\mathrm{TMTSF}\right)\mathrm{}}_{2}X$, $X^{-}$ = ${\mathrm{AsF}}_6^{-}$ and P${\mathrm{F}}_6^{-}$ to be members of a family with quite similar physical properties. The data are discussed on the basis of Overhauser's treatment of itinerant antiferromagnetism.