Effective Hamiltonians for pseudo-one-dimensional compounds of the type AFeX3

In the past various effective Hamiltonians have been used to describe the properties of pseudo-one-dimensional compounds of the type CsFeX3 and RbFeX3 where X is Cl or Br. In the models the number of electronic levels considered have varied from 3 to 25 and some models have included a correlated effective field to incorporate the effects of intrachain exchange interactions. These models are used in fitting the variations of quadrupole splitting with temperature and the results are compared. (orig.)