Magnetic Torque due to Anisotropic Diamagnetism in Neutral BEDT-TTF Crystals

Magnetic susceptibility and torque measurements have been performed for neutral BEDT-TTF crystals to investigate the diamagnetic properties. The diamagnetic susceptibility is found to be anisotropic at room temperature, −1.9 × 10−4 emu/mol for the magnetic field \(H\parallel [011]\) and −2.5 × 10−4 emu/mol for \(H\parallel [100]\), comparable to the Langevin diamagnetism estimated from the Pascal constants, −2.04 × 10−4 emu/mol. The diamagnetism for both directions is gradually enhanced with decreasing temperature. Sinusoidal torque curves are clearly observed for two field rotations in the \((0\bar{1}1)\) and (100) planes, reflecting the anisotropic diamagnetism of the neutral BEDT-TTF molecule. The results show that careful attention must be paid to quantitative discussion of the torque signals in various organic materials.