Local magnetic moments in iron and nickel at ambient and Earth's core conditions

TL;DR

This paper reveals that the interplay of band-structure effects and Coulomb interactions creates local magnetic moments in iron and nickel, impacting their magnetic properties at Earth's core conditions and challenging existing theories.

Contribution

It demonstrates that band-structure effects combined with Coulomb repulsion are key to understanding magnetism in iron and nickel under extreme conditions.

Findings

Nickel's van Hove singularity affects its magnetism.

Electron scattering in nickel is linear in temperature, violating Landau theory.

Iron remains a good Fermi liquid at Earth's core pressures.

Abstract

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.