Magnetic Torque Studies in Two-Dimensional Organic Conductor λ-(BETS)2FeCl4

Systematic measurements of the magnetic torque τ of the organic conductor λ-(BETS)2FeCl4 have been performed to investigate the magnetic properties. In the magnetic field dependence of τ, a very sharp structure is observed at ∼1.2 T, resulting from the spin-flop transition. A step-like behavior associated with small hysteresis appears at ∼10 T, which is caused by the antiferromagnetic insulator–paramagnetic metal (AFI–PM) transition. In the angular dependence of τ for magnetic fields in the b*–c plane, it is found that the zero-crossing angles significantly change with field and temperature. The changes provide reasonable evidence of the antiferromagnetic order of the π spins (not the Fe 3d spins) in the AFI phase. The AFI–PM transition field has a minimum when the magnetization of the 3d spins has a maximum as a function of field angle.