Susceptibility critical behaviour

Quantitative agreement, of course, is not to be expected, as this critical intensity is not susceptible of exact definition at all. The comparison shows that the intensities for which the quadratic law is transformed into the linear law are of the order of magnitude anticipated, and also that the behaviour at different temperatures becomes intelligible. 

The temperature behaviour of a typical ferrimagnet is shown in Fig. 7.15. Notice a considerable non-linearity of the 1/x versus T curve near the critical temperature. Above the ordering temperature the susceptibility obeys a relationship Neel hyperbola)... 

The temperature dependence of susceptibility or, more accurately, the inverse of susceptibility is a good characterisation parameter. A small, negative, constant value. Fig. 4.7, corresponds to a diamagnetic material a linear relationship is shown by a paramagnetic material. In some metals, known as Pauli paramagnets, a small, positive, constant susceptibility is observed. Some other materials show linear behaviour only for high temperatures below a critical temperature, their susceptibility shows a complex behaviour. They are called ferro-, ferri- or antiferromagnets. 

Information about the magnetic behaviour of heavy-fermion systems is contained in the wavenumber- and frequency-dependent magnetic susceptibility x q, v). In less strongly correlated metals, x is usually expressed via Stoner s formula [for critical reviews on itinerant magnetism and Stoner theory see, e.g., Moriya (1979), Gautier (1982), Stamp (1985)],... 

The Goldstone mode does not show the explicit temperature dependence (in reality, parameters K, qo, p depend on temperature but not critically) and the total susceptibility manifests a quasi Curie type behaviour at temperature T h with a cusp of amplitude... 

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