Spin density waves in organic metals (invited)

The magnetic properties of the (TMTSF)2X family of organic conductors are reviewed. Susceptibility, ESR, and NMR measurements have led to the conclusion that the metal-insulator transition for X = PF-6, AsF-6, and SbF-6 is driven by the onset of a spin density wave. Near the transition temperature (TSDW), the ESR line shifts, broadens, and rapidly loses intensity. In the semiconducting phase of (TMTSF)2PF6 the static susceptibility is anisotropic and reveals a spin-flop transition at 6 kG. The increase in the proton NMR linewidth yields a value for the SDW amplitude of μ/μB∼ 10-1, in rough agreement with the prediction of mean field theory. Fluctuations near TSDW contribute to proton spin-lattice relaxation.