Spin-density wave fluctuation

This argument breaks down when charge fluctuations are suppressed in favour of spin-density wave fluctuations. As described in Chapter 5 this occurs in the intermediate-coupling regime, around U At. 

I = insulator, s.c. = semiconductor, cond. = conductor, AF = antiferromagnetic, F = ferromag-net, scf = strong-correlation fluctuations, J-T = cooperative Jahn-Teller orbital ordering, LS = J-T that maximizes orbital angular momentum, dis. = disproportionation 2(j = e + e, SDW/ CDW = spin/charge-density wave. 

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). 

We see that the spin fluctuations are to some extent phonon-like, with an energy proportional to the wave vector, q. Such excitations are often called paramagnons . The function 2 Im x( , (o) is referred to as the spectral density of the paramagnons, often denoted by A q, co). 

---