Characterization of ferrimagnetic Heisenberg chains according to the   constituent spins
  The low-energy structure and the thermodynamic properties of ferrimagnetic Heisenberg chains of alternating spins $S$ and $s$ are investigated by the use of numerical tools as well as the spin-wave theory. The elementary excitations are calculated through an efficient quantum Monte Carlo technique featuring imaginary-time correlation functions and are characterized in terms of interacting spin waves. The thermal behavior is analyzed with particular emphasis on its ferromagnetic and antiferromagnetic dual aspect. The extensive numerical and analytic calculations lead to the classification of the one-dimensional ferrimagnetic behavior according to the constituent spins: the ferromagnetic ($S>2s$), antiferromagnetic ($S<2s$), and balanced ($S=2s$) ferrimagnetism. 
Shoji Yamamoto, Takahiro Fukui and Toru Sakai