Susceptibility of the Spin 1/2 Heisenberg Antiferromagnetic Chain
  Highly accurate results are presented for the susceptibility, $\chi (T)$ of the $s=1/2$ Heisenberg antiferromagnetic chain for all temperatures, using the Bethe ansatz and field theory methods. After going through a rounded peak, $\chi (T)$ approaches its asympotic zero-temperature value with infinite slope. 
Sebastian Eggert, Ian Affleck, Minoru Takahashi