Determination of the high-spin mole fraction

A thermally induced spin transition is characterised by an xHs = f(T) curve with 

X-ray diffraction cell parameters, interatomic distances low high 

T /i) is identified with a temperature at which xHs = ls = 1/2. Various types of xHS versus T curves have been observed in the solid state and can be classified as follows (Fig. 9.1)  

Sometimes the transition curve depends upon the starting point of heating/ cooling, rate of heating/cooling and the number of cycles of heating/cooling. 

The construction of the xHS versus T curve on the basis of magnetic susceptibility measurements is very simple. In the pure LS or HS state the product xT is a constant when the Curie law is obeyed (for pure LS Fe(II) systems this becomes zero if the corrections to underlying diamagnetism and temperature-independent paramagnetism were properly made). Thus the mole fraction of the HS state can be expressed as (Fig. 9.2) 

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