Pauli-like paramagnetism

The magnitude of the thermopower (as well as of the Pauli paramagnetism) at high temperature is a measure of the density of states at the Fermi level, and therefore it is expected to be inversely proportional to the bandwidth. In fact, as seen in Table 2.6, a fairly good correlation exists between the observed increase in the perylene intermolecular distances (all with the same type of overlap) and the increase in the high temperature thermopower (and Pauli-like paramagnetism) in this family of compounds. 

Fig. 2. Temperature dependence of the magnetic susceptibility x (right scale) and of the field for Pd NMR at fixed Larmor frequency Bo (left scale) for palladium. Similar to Fig. la, the NMR field shift and the susceptibility are proportional. Both are (mainly) caused by the Pauli-type paramagnetism of the d-like conduction electrons. (The temperature dependence is not predicted by the simple free-electron description of the susceptibility in metals.) [Reproduced with permission from Seitchik et al. (16). Copyright 1964 American Physical Society.]...

The susceptibility data cannot be simply described as Curie-like susceptibility at lower temperatures and temperature-independent Pauli-like susceptibility at higher temperatures [441]. Some unusual transitions were observed in the temperamre dependence of susceptibility, for example paramagnetic susceptibility decreased gradually with lowering temperature, which suggests the coexistence of polarons and spinless bipolarons and the possible formation of bipolarons with changing temperature or doping level. 

At room temperature the paramagnetic susceptibility of this compound is small (3.4 x 10 " emu/mol), only slightly larger than the Pauli-like contributions in many molecular conductors. The two-phase transitions are seen in static magnetic susceptibility measurements as two decreasing steps of the susceptibility upon cooling with similar hysteresis (Figure 2.50). The first... 

Step can be a decrease of the Pauli-like contribution of the conduction electrons, but the second one is more probably associated with a reduction of temperature-independent paramagnetism of the inorganic polymeric chains. Just below the second transition a residual value of 1.8 x lO " emu/mol is observed, probably indicative of a temperature-independent paramagnetism, and upon further cooling an increase of the susceptibility due to a Curie tail is observed. This tail shows an increase as with a = 0.6, an exponent that is indicative of disorder [98—100], most probably associated with the solvent. Since this compound is EPR silent no further indications on the origin of the observed susceptibility can be taken from these data alone. 

Also as in Per2Au(mnt)2, the EPR lines of these compounds are relatively narrow (0.5 G in i-mnt and 1 G in i-mns compounds) and have g-values corresponding to the perylene molecule [79]. The static magnetic susceptibility of the Per2Au(i-mns)2 compound shows a small Pauli-like temperature-independent paramagnetism, 1.6 x 10 emu/mol [108], comparable to that of Per2Au(mnt)2. 

Hund s rule, like the Pauli exclusion principle, is based on experiment It is possible to determine the number of unpaired electrons in an atom. With solids, this is done by studying their behavior in a magnetic field. If there are unpaired electrons present the solid will be attracted into the field. Such a substance is said to be paramagnetic. If the atoms in the solid contain only paired electrons, it is slightly repelled by the field. Substances of this type are called diamagnetic. With gaseous atoms, the atomic spectrum can also be used to establish the presence and number of unpaired electrons. 

PrFe4Sbj2 is likely a metal. Magnetic measurements on polycrystalline samples that were about 90% phase pure indicated ferromagnetic ordering below 5 K with a moment of 1 /i per formula unit. The only other phase detected using X-ray diffraction was FeSb2, which has a weak Pauli paramagnetic susceptibility (Dannebrock et al., 1996). 

We should then formulate C0P3 either as (Co )4(P4 )3 or as a covalent compound Co4(P4)3 in the latter case each metal atom would acquire a share in nine electrons, since each P4 group is a source of 12 electrons. The Co atom in C0P3 would thus attain the Kr configuration like Fe in FeSj. Just as CoSj with the pyrites structure has an excess of one electron per metal atom, so this would be true of Ni in NiP3, accounting for the metallic conduction and Pauli paramagnetism of the latter. 

The decrease in conductivity in polytoluidines can be attributed to their electronic structure. The electronic structure of polytoluidines, like PANI, corresponds to that of a metal with the highest occupied band three quarters filled. The observation of Pauli paramagnetism in polytoluidines [39,40] reveals the existence of a degenerate electronic structure with a finite density of states at the Fermi energy as in PANI [117]. Note that PANI also typically does not exhibit the traditional signatures of metallic transport due to a combination of... 

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