Hysteretic magnetic state in the organic τ-phase conductors

The τ-phase conductors are known to exhibit resistance upturn and negative magnetoresistance below Tmin50 K. Well below Tmin, at least in the range of about 1 to several K, a large hysteresis in the field sweep as well as angle sweep is observed in the configuration of current, I∥ or I⊥, and magnetic field, with B∥ or B⊥, where ∥ and ⊥ refer to the two-dimensional a-b plane. Furthermore, with I⊥ and BI, symmetry of the angular dependence of magnetoresistance varied between four-fold and two-fold depending on the region of T and B. Two-fold symmetry is hard to understand from the symmetry of the crystal and the relevant Fermi surface. Although many of the phenomena are unexplained, we believe that we have observed a new type of electronic property.