ABSTRACT
Advances in the theory of spin fluctuations have resulted in a remarkable synthesis of the microscopic spin dynamics and the bulk properties of weak ferromagnets and exchange enhanced paramagnets. The self-consistent renormalisation (SCR) theory of spin fluctuations has been developed from these by Moriya and has been extended and applied to a number of weak ferromagnets by G. G. Lonzarich and L. Taillefer. The SCR theory of spin fluctuations appears to give a full account of the both the static and dynamical properties of weak ferromagnets and exchange enhanced para-magnets. In the case of systems like YMn2 and ß-Mn, which display antiferromagnetic spin fluctuations, it appears that topological frustration is an important extra factor, leading to quantum spin liquid behaviour. Further theoretical insight is needed into the treatment of frustration in the context of itinerant electron magnetism. Inelastic neutron scattering and muon spin research have important and complementary roles in characterising the spin dynamics in these intriguing magnetic materials.
