The Dimer Pair. Singlet-Triplet Behavior

A one-dimensional magnetic chain may be conceptually formed by bringing together N molecules, each with spin S. The general interaction between each of the sites may be summarized in the Hamiltonian 

Equation 37 is often modified in order to model experimental results more realistically and/or make theoretical calculations more manageable. One common modification is the alternating chain where the exchange integral between sites in the chain alternate between J and J (58, 181). This model is particularly applicable to a chain composed of dimers with each molecule of the dimer having spin S. In the limit J J - 1, the model reduces to the Heisenberg chain. When J J 0, the model reduces to a set of isolated 

Another modification that has been examined extensively is decomposition of the vector spin into x, y, and z components  

In the last seven years, the demonstration of one-dimensional antiferromagnetic behavior in [(CHs)4N][MnCl3] (TMMC) (125), CsMnCl3(H20)z (378), and related systems (see Part II) has led to increased experimental and theoretical work in the field (49, 199, 297). More recently, a number of one-dimensional systems with ferromagnetic coupling have been reported, in particular, CsNip3(16, 257, 384, 385) and RbFeCl3(l, 311). 

TEMPERATURE DEPENDENCE OF SUSCEPTIBILITY FOR THREE-DIMENSIONAL MAGNETIC MATERIALS  

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