Atomic additive contributions paramagnetic susceptibility

It is often found that the Curie law Eq. (21) is followed by many magnetically dilute substances other than free atoms or ions. There is, in addition, a second-order contribution to the paramagnetic susceptibility, the so-called temperature-independent paramagnetism Not. (also abbreviated TIP, cf. section 1,1.3.6) which arises from states separated from the ground state by an energy k T It follows that the molar susceptibility corrected for diamagnetism may be frequently represented by the Langevin-Debye expression... 

The rules for the electron-pair bond were divided in two classes. In the first, Pauling summarized the conclusions of Heitler and London s work in three postulates, which he considered to express essentially the quantum mechanical underpinning of Lewis s 1916 results that the formation of an electron-pair bond results from the interaction of an unpaired electron coming from each of two atoms (as mentioned previously, Lewis objected to the specification of the electron s provenance) that in bond formation, the spins of the interacting electrons are antiparallel so that they do not contribute to the paramagnetic susceptibility of the compound and that two electrons forming a shared bond cannot participate in the formation of additional pairs. 

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... 

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