Antiferromagnetic Ordering in the Organic Conductorbis-Tetramethyltetraselenafulvalene-Hexafluorophosphate [(TMTSF)2-PF6]

The anisotropy in the static susceptibility of ${\mathrm{}\left(\mathrm{TMTSF}\right)\mathrm{}}_2$-P${\mathrm{F}}_6$ has been investigated above and below the metal-insulator transition for a range of fields between 4 and 25 kOe. The results are consistent with the occurrence of an Overhauser antiferromagnetic transition to a spin-density-wave state with an easiest axis perpendicular to the stacks. Below the transition, evidence for a spin-flop transition is seen. Above the transition, evidence for a crossover, possibly from $n=3\mathrm{}$ to $n=1\mathrm{}$ spin behavior, is seen.