Field-orientation dependence of magnetoresistance of a double-column organic conductor, (DMET)2ClO4

An organic conductor, (DMET)2ClO4 (DMET = dimethyl(ethylenedithio)diselenadithiafulvalene), has two types of DMET columns along the a-and b-axes of the crystal lattice, respectively. The salt undergoes a metal-to-semiconductor transition at 32 K. Its resistivity and thermopower both along the a-and b-axes show anomalies at 18 and 7 K in addition to that at 32 K. Magnetoresistance along the c*-axis was measured while rotating the magnetic field within the ab plane above and below temperatures of the anomalies. The identification of the column that is mainly related to each anomaly is tried using the change in the peak position of the field-orientation dependence of the magnetoresistance. The resistivity along the c*-axis and thermopower along the c-axis show anomalies at 70 and 110 K in addition to those at low temperatures.