Unconventional Hund Metal in a Weak Itinerant Ferromagnet

TL;DR

This study investigates magnetic fluctuations in MnSi, revealing evidence of Hund metal behavior and non-Fermi liquid properties, advancing understanding of weak itinerant ferromagnets through neutron scattering and many-body theory.

Contribution

It provides experimental evidence of Hund metal characteristics in MnSi and clarifies the role of interorbital Hund's exchange in weak itinerant ferromagnets.

Findings

Short-wavelength magnons propagate until a mode crossing occurs.

Local susceptibility peaks at a coherence energy consistent with Hund metal theory.

Electron scattering with orbital and spin fluctuations explains non-Fermi liquid behavior.

Abstract

The physics of weak itinerant ferromagnets is challenging due to their small magnetic moments and the ambiguous role of local interactions governing their electronic properties, many of which violate Fermi liquid theory. While magnetic fluctuations play an important role in the materials' unusual electronic states, the nature of these fluctuations and the paradigms through which they arise remain debated. Here we use inelastic neutron scattering to study magnetic fluctuations in the canonical weak itinerant ferromagnet MnSi. Data reveal that short-wavelength magnons continue to propagate until a mode crossing predicted for strongly interacting quasiparticles is reached, and the local susceptibility peaks at a coherence energy predicted for a correlated Hund metal by first-principles many-body theory. Scattering between electrons and orbital and spin fluctuations in MnSi can be understood at the local level to generate non-Fermi liquid character. These results provide crucial insight into the role of interorbital Hund's exchange within the broader class of enigmatic multiband itinerant, weak ferromagnets.