Magnetic Properties of Single-Crystals of the S=2 Quasi-1D Heisenberg Antiferromagnet MnCl3(bpy)

Recent theories have revealed topological differences between one-dimensional (1D) Heisenberg antiferromagnets (HAFs) with odd and even integer spins (S). With this renewed interest, we have investigated the low-field magnetic susceptibility, specific heat, and high-field magnetization of single-crystal samples of MnCl3(bpy), bpy=2,2t-bipyridine, which is regarded as an S = 2 quasi-1D HAF. With the magnetic field oriented along the a*, b and c directions, the magnetic susceptibilities possess broad maxima around 100K. When the magnetic field is parallel to the b-axis, a sharp peak at 11K is observed in the magnetic susceptibility, while a smaller feature is detected in the specific heat, indicating a transition to long-range antiferromagnetic order. At 1.7K, the high-field magnetization curve along the c-axis shows a spin-flop transition, while the responses in the other directions show monotonic increases. These experimental findings confirm that MnCl3(bpy) is not an ideal model system to study the S=2 Haldane phase.