Static magnetic susceptibility in (TMTTF) 2Br and (TMTSF) 2AsF 6

We report on the static magnetic susceptibility in the spin density wave (SDW) phase of (TMTTF) ₂Br and (TMTSF) ₂AsF ₆. A decrease of the differential susceptibility of (TMTSF) ₂AsF ₆ was observed around 4 K. This anomaly indicates a difference of the spin canting above and below the critical temperature. In the measurements of magnetic susceptibility on the commensurate SDW phase of (TMTTF) ₂Br, a large decrease of the spin susceptibility was observed above T_SDW and non-activated-type behavior in the b′-axis susceptibility was observed below the spin-flop field at low temperature. The data are discussed on the basis of commensurability.