Magnetic Order in Organic Dirac Electron System alpha-(BETS)(2)I-3

Magnetic torque measurements were conducted to investigate the magnetic properties of organic conductor alpha-(BETS)(2)I-3, a candidate material that forms Dirac electron states under ambient pressure, and alpha-(BEDT-TTF)(2)I-3, where Dirac fermions are realized under high pressure. In alpha-(BEDT-TTF)(2)I-3, magnetic torque reflecting the anisotropic diamagnetism is observed in the nonmagnetic charge-ordered state. The complex torque curves of alpha-(BETS)(2)I-3, observed only at low temperatures and low magnetic fields, provide the first evidence for the existence of magnetic order. The clear change in the torque amplitude observed at the metal-insulator crossover temperature suggests that this crossover is related to the magnetic nature of alpha-(BETS)(2)I-3.