Long-range magnetic order and interchain interactions in the $S=2$ chain   system MnCl$_3$(bpy)
  A compound with very weakly interacting chains, MnCl$_3$(bpy), has attracted a great deal of attention as a possible $S=2$ Haldane chain. However, long-range magnetic order of the chains prevents the Haldane gap from developing below 11.5~K. Based on a four-sublattice model, a description of the antiferromagnetic resonance (AFMR) spectrum up to frequencies of 1.5~THz and magnetic fields up to 50~T indicates that the interchain coupling is indeed quite small but that the Dzaloshinskii-Moriya interaction produced by broken inversion symmetry is substantial (0.12~meV). In addition, the antiferromagnetic, nearest-neighbor interaction within each chain (3.3~meV) is significantly stronger than previously reported. The excitation spectrum of this $S=2$ compound is well-described by a $1/S$ expansion about the classical limit. 
Randy S. Fishman, Shin-ichi Shinozaki, Akira Okutani, Daichi   Yoshizawa, Takanori Kida, Masayuki Hagiwara, and Mark W. Meisel
cond-mat.mtrl-sci