Van-Vleck type paramagnetism

In EuN and EuP Jq = 0, therefore only a weak Van Vleck-type paramagnetism corresponding to the second term in eq. (33.10) is to be expected. Traces of divalent Eu therefore will render any x(T) measurement unreliable. Junod et al. (1969) indicate that the experimental susceptibility data are 25% higher than calculated, without however presenting the x curves. 

The heat capacity behavior of PrNi2 confirms that it becomes a Van Vleck paramagnet at low temperatures (65). It exhibits no X-type thermal anomaly expected if there is magnetic ordering only a Schottky-type heat capacity excess is observed. This is a consequence of the thermal population of the higher crystal field states. 

The results show that the magnetic susceptibility of these carbides agrees well with a Curie-Weiss law of the form X = Xq + (C/T — 0 ) above the temperature T. The only exception is samarium hypocarbide, for which a deviation from this law has been observed. This type of deviation also occurs in SmC2 and has been attributed to Van Vleck paramagnetism. 

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