Exactly solvable su(N) mixed spin ladders
  It is shown that solvable mixed spin ladder models can be constructed from su(N) permutators. Heisenberg rung interactions appear as chemical potential terms in the Bethe Ansatz solution. Explicit examples given are a mixed spin-1/2 spin-1 ladder, a mixed spin-1/2 spin-3/2 ladder and a spin-1 ladder with biquadratic interactions. 
M.T. Batchelor, J. de Gier and M. Maslen