  Some Bravais lattices have a particular geometry that can slow down the
motion of Bloch electrons by pre-localization due to the band-structure
properties. Another known source of electronic localization in solids is the
Coulomb repulsion in partially filled d- or f-orbitals, which leads to the
formation of local magnetic moments. The combination of these two effects is
usually considered of little relevance to strongly correlated materials. Here
we show that it represents, instead, the underlying physical mechanism in two
of the most important ferromagnets: nickel and iron. In nickel, the van Hove
singularity has an unexpected impact on the magnetism. As a result, the
electron-electron scattering rate is linear in temperature, in violation of the
conventional Landau theory of metals. This is true even at Earth's core
pressures, at which iron is instead a good Fermi liquid. The importance of
nickel in models of geomagnetism may have therefore to be reconsidered.
