Band structure and magnetic fluctuations in ferromagnetic or nearly ferromagnetic metals

High precision studies of the band structure near the Fermi level in ferromagnetic and nearly ferromagnetic metals have been carried out by means of De Haas-Van Alphen effect which measures Fermi surface areas, cyclotron masses and scattering lifetimes for separate majority and minority spin carriers in an applied magnetic field. Semi-empirical bands fitted to accurate De Haas-Van Alphen data may be used as inputs to modern theories of metallic magnetism which take account of both independent quasiparticles and enhanced magnetic fluctuations. This paper summarises recent De Haas-Van Alphen studies in metals which are examples of incipient, weak, and strong ferromagnetism, respectively. In the archetypal weak itinerant ferromagnet Ni 3Al, which we have investigated both by means of the De Haas-Van Alphen effect and inelastic neutron scattering, a detailed analysis of the roles of independent particle excitations and enhanced magnetic fluctuations is presented. A simple theoretical model is shown to yield, in terms of empirically determined microscopic parameters only, a good quantitative description of the low temperature magnetic equation of state in this material.