Van Vleck temperature-independent paramagnetism

Many of the Th nitrides are more or less stable at elevated temperatures, electrically and thermally insulating, and have an extremely weak (Van Vleck) temperature-independent paramagnetism. The face-centered cubic (fee) mononitride, ThN, is an important exception. It is metallic. It has a weak temperature-independent (Pauli) paramagnetism. Subsequent comparison of the electronic properties will show many simularities between ThN and metallic Th. An appreciable metallic bonding is also indicated by anomalously large interatomic distances in ThN. 

It is assumed that the measured magnetic susceptibility has already been corrected for the underlying diamagnetism (usually using the set of Pascal constants) and also for the temperature-independent paramagnetic (van Vleck) term (its mononuclear estimate being multiplied by the number of magnetic centres). 

Another additive term in the magnetic susceptibility arises from the temperature-independent core diamagnetism of all the ions in a solid. For YBa2Cu307 the core diamagnetism is approximately -2 x 10 7 based on a calculation using Pascal s constants (9). This small negative contribution serves to reduce the total susceptibility. A third possible contribution arises from Van Vleck paramagnetism (10) caused by excited states in the atoms of the... 

Here ps is the Bohr magneton, p is the effective number of Bohr magnetons, and ks is Boltzman s constant. Thus a plot of 1 // versus temperature is a straight line with an intercept at zero. Other contributions to the susceptibility of an isolated molecule include core diamagnetism and Van Vleck paramagnetism, both of which are small and temperature independent (231). 

For Sm2Fei2P7 Van Vleck paramagnetism is observed. Such temperature-independent contributions to the susceptibilities can also be assumed for the Sm + and Eu + ions... 

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