Unconventional Hund metal in a weak itinerant ferromagnet

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 its 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.

Neutron spectroscopy evidence on the dual nature of magnetic excitations in a van der Waals metallic ferromagnet Fe$_{2.72}$GeTe$_{2}$

“…To account for the magnetism in these materials, there is a third scenario intermediate between the two aforementioned cases, where some d-electrons are itinerant, while the others are localized, and there is interplay between the local moments and itinerant electrons which provide the Kondo screening 23 . The situation is then similar to that found in heavy fermion systems with more localized f electrons [24][25][26] , but is more controversial due to the more itinerant nature of d electrons 14,[27][28][29][30][31][32][33][34][35][36][37][38] . This is particularly the case for iron-and copper-based high-temperature superconductors [30][31][32][33][34][35][36][37][38][39][40][41][42][43] .…”

High-energy magnetic excitations from heavy quasiparticles in CeCu$_2$Si$_2$

“…Consistent with previous observations [18,35,37], the magnetic excitations are dispersive for E 1.5 meV, but at higher energies they form a column in energy away from the zone boundary. Such an evolution from dispersive to columnar magnetic excitations is unexpected for a local-moment magnetic system, but have been observed in itinerant magnetic systems, including heavily hole-doped iron pnictides [50], Fe-doped MnSi 3 [51] and MnSi [52].…”

Uncovering Non-Fermi-Liquid Behavior in Hund Metals: Conformal Field Theory Analysis of an SU(2)×SU(3) Spin-Orbital Kondo Model

“…The normal state of Hund metals is of great interest on its own, since it typically shows bad-metal behavior [6,15,16]. Motivated by these considerations, computational and experimental studies of Hund metals have begun to uncover their rich physics in recent years [4,5,8,11,12,[17][18][19][20][21]. When studying Hund metals in the context of dynamical mean-field theory (DMFT), the problem of a crystal lattice with many strongly interacting lattice sites is mapped onto a "Hund impurity," coupled self-consistently to an effective noninteracting metallic bath.…”