Curie-Weiss behaviour

Magnetic properties metals up to plutonium are Pauh magnets and Curie-Weiss behaviour starts with curium ... 

Curie-Weiss behaviour from 309 to 83 K with a Weiss constant 6 s 10 K. The 3-carboxylate was studied in the range 275-4.2 K and the data were interpreted in terms of an antiferromagnetic interaction between silver ions using the Ising linear chain model. This gave an exchange energy of / = —30.8 1.0 cm-1 and g = 2.5 0.02 which was somewhat smaller than the experimentally determined (g) of 2.08.513... 

The determination of n from measurement of peff is the most familiar application of magnetic susceptibility measurements to inorganic chemists. To the extent that the spin-only formula is valid, it is possible to obtain the oxidation state of the central atom in a complex. Thus an iron complex with a peff of 5.9B.M. certainly contains Fe(III) (high-spin d5) and not Fe(II). The diamagnetism of AgO rules out its formulation as silver(II) oxide, because Ag2+ has an odd number of electrons (d9) and should be paramagnetic it contains Ag(I) and Ag(III), in equal amounts. There are, however, a number of pitfalls, especially if reliance is placed on a single measurement at room temperature. The Curie law is rarely obeyed within the limits of experimental error. This means that the measured peff is somewhat temperature-dependent. A number of factors can be responsible for deviations from ideal Curie (or even Curie-Weiss) behaviour, and/or from the spin-only formula. 

Uranium(v) compounds are, as expected for an f system, paramagnetic, usually exhibiting Curie-Weiss behaviour, with large Weiss constants g-values, expected to be 6/7, are modified by the mixing in of higher states and by orbital-reduction effects (covalency), experimental -values including values of 1.2 in NasUFg and 0.71 in CsUFe. 

Fig. 4.11. Temperature dependence of the inverse susceptibility fon (a) a ferromagnetic solid, showing a spontaneous magnetisation (ot T Tc (b) an antiferromagnetic material 7J is the Neel temperature. (Adapted from Cullity, 1972.)...

Figure 11.18 The Curie-Weiss behaviour of a ferroelectric solid above the Curie temperature T. Note relative permittivity T, absolute temperature...

There is no Curie-Weiss behaviour immediately above but only at a much higher temperature, the Bums temperature, T. Between and the relationship between the relative permittivity and the temperature is usually better described by a quadratic law ... 

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