High field studies on the novel antiferromagnetic states of the organic conductor α-(BEDT-TTF)₂KHg(SCN)₄

We present the magnetization and Hall effect measurements at high fields perpendicular to the conducting plane of α-(BEDT-TTF)₂KHg(SCN)₄, in order to get more detailed insight into the magnetic phase diagram which we have previously proposed from the magnetoresistance measurements. The magnetization curve shows a remarkable hysteresis in the same field range where the magnetoresistance does. The de Haas-van Alphen oscillations superimposed on these magnetization are essentially reversible and drastically enhanced above the high field phase boundary. Standard analysis on the Lifshitz-Kosevich theory show no field-dependence of the effective mass, essentially constant of 1.6m₀ up to above the phase boundary, but that the Dingle temperature changes from 4K to 15K discontinuously at the phase boundary. The Hall resistance shows the prominent non-linear behavior at high fields above 10T. These results are discussed and compared with those by other groups.