Singlet magnetism in intermetallic UGa$_2$ unveiled by inelastic x-ray scattering

TL;DR

This study uncovers the atomic-scale electronic excitations and singlet magnetism in intermetallic UGa$_2$ using advanced inelastic x-ray scattering, revealing its quantum magnetic nature and the local 5f^2 configuration.

Contribution

It demonstrates the use of high-resolution inelastic x-ray scattering to identify atomic excitations and elucidate the magnetic ground state in UGa$_2$, advancing understanding of uranium intermetallics.

Findings

Atomic excitations are highly atomic in nature.

The ground state involves a $ ext{Γ}_1$ singlet and/or $ ext{Γ}_6$ doublet.

Magnetism arises from mixing of excited states due to inter-site exchange.

Abstract

Using high resolution tender-x-ray resonant inelastic scattering and hard-x-ray non-resonant inelastic scattering beyond the dipole limit we were able to detect electronic excitations in intermetallic UGa$_2$ that are highly atomic in nature. Analysis of the spectral lineshape reveals that the local $5f^2$ configuration characterizes the correlated nature of this ferromagnet. The orientation and directional dependence of the spectra indicate that the ground state is made of the $\Gamma_1$ singlet and/or $\Gamma_6$ doublet symmetry. With the ordered moment in the $ab$ plane, we infer that the magnetism originates from the higher lying $\Gamma_6$ doublet being mixed with the $\Gamma_1$ singlet due to inter-site exchange, qualifying UGa$_2$ to be a true quantum magnet. The ability to observe atomic excitations is crucial to resolve the on-going debate about the degree of localization versus itineracy in U intermetallics.