Symmetry Change in the Angular Dependence of Magnetoresistance of the Two-Dimensional Organic Conductor, τ-(EDO-S, S-DMEDT-TTF)2(AuBr2)(AuBr2)y, (y-- 0.75)

Angular dependence of magnetoresistivity, ρ c (φ), of a quasi-two-dimensional organic conductor, τ-(EDO- S , S -DMEDT-TTF) 2 (AuBr 2 )(AuBr 2 ) y , ( y ∼0.75), where EDO- S , S -DMEDT-TTF is ethylenedioxy- S , S -dimethylethylenedithio-tetrathiafulvalene, was measured for the magnetic field and the electrical current parallel and perpendicular to the most conducting a b plane. The magnetoresistance is negative in the semiconducting range below about 50 K. It was found that the period of ρ c (φ) changes from 90° at 5.0 T to 180° at 0.5 T and the principal axis of ρ c (φ) at 0.5 T depends on the field-orientation at 5.0 T. The change in the period and the principal axis of ρ c (φ) is discussed in terms of formation and reorientation of magnetic domains.