Magnetic torque of lambda-(BETS)(2)FeCl4

Magnetic torque of lambda-(BETS)(2)FeCl4 is measured up to 15 T and down to 0.4 K. Clear first-order spin flop transition between the antiferromagneti c (AF) and the canted antiferromagnetic (CAF) phases is observed in the mag netic field of about 1.2 T and below 9.5 K. The AF easy axis is found to be in the direction tilted by about 30 degrees from the c-axis to the b*-axis , which is different from the previous reports on the easy axis (the c-axis ). At the steplike transition with hysteresis around H = 10 T between CAF a nd the field induced ferromagnetic (F) (paramagnetic) phases, the direction of the magnetic easy ads changes. The two transitions on the H - T phase d iagram are considered on the basis of the coupled two spin system; Fe3+ (S = 5/2) and (BETS)(2) (S = 1/2).