Spin fluctuation theory

For spin fluctuation systems, the best example is again UAl2 In fact as shown in Fig. 3 it is the unique example where T InT dependence at low temperature, predicted by spin fluctuation theory, has been in practice observed (very recently, such behaviour... 

According to the spin fluctuations theory, the Curie temperature of the band ferromagnets is inversely proportional to the density of states in the subbands near the Fermi level, NT(Ef) and Nl(E ). The increase of the lattice parameters after the hydrogen atoms incorporation to the lattice induces the decrease of the degree of wave-function hybridization between the 3r/-electrons of Fe atoms and 5r/-electrons of rare-earth metal atoms. This in turn entails the decrease of density of states in both zones NT(Ef) and Ni(EF). 

Using the notions of spin-fluctuation theory, the approach to the magnetic instability can be understood as a critical slowing down of the fluctuations accompanied by a gradual decrease of TSF. The deviation from Curie-Weiss law should... 

The study of spin fluctuations in clusters and the resulting temperature dependence of the magnetic properties is a subject of considerable current interest. In this section we discuss results derived from the spin-fluctuation theory described in Section 6.2.2 which takes into account both the fluctuations of the magnetic moments and the itinerant character of the d electron states. 

Recently spin fluctuations (Moriya and Kawabata, 1973a,b) which are characterized by electron correlations turned out to be important for describing the susceptibility, electrical-, thermal- and magneto-resistivities of itinerant ferro-magnets. Moriya (1976) pointed out that the thermodynamic properties of itinerant ferro- and antiferromagnets are mainly governed by the exchange enhanced spin fluctuation modes. At present the results of the spin fluctuation theory can account for the Curie-Weiss susceptibility without localized mo-... 

Fig. 16. Temperature dependence of the electron specific heat coefficient for UPtj. The solid line is calculated from spin fluctuation theory, the dashed line is the phonon-subtracted experimental data of Renker et al. (1986).

We now turn to a discussion of the Neel temperature. Our estimated Stoner temperature for UCuj is 1000 K. Given the experimental value of 15K, this implies that Tn is totally controlled by spin fluctuation effects, as observed for a number of transition metal magnets. This prompted us to calculate using spin fluctuation theory (Lonzarich 1986, Moriya 1987). For antiferromagnets, this formalism has been derived by Nakayama and Moriya (1987). The only change we make is to replace the assumed form of the susceptibility of Nakayama and Moriya by the Lorentzian form observed in neutron scattering. 

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