Determination of spin and orbital magnetization in the ferromagnetic superconductor UCoGe

TL;DR

This study combines experimental techniques and calculations to accurately determine the spin and orbital magnetic moments in the ferromagnetic superconductor UCoGe, revealing the nature of its magnetic electrons.

Contribution

It provides the first detailed experimental separation of spin and orbital moments in UCoGe, highlighting the itinerant character of U 5f electrons and emphasizing the importance of measuring both moments for understanding 5f systems.

Findings

U 5f electrons carry a spin moment of approximately -0.30 μ_B

The orbital moment is about 0.40 μ_B, with U and Co moments antiparallel

The U moment is itinerant, with a ratio U_l/U_s of about -1.3

Abstract

The magnetism in the ferromagnetic superconductor UCoGe has been studied using a combination of magnetic Compton scattering, bulk magnetization, X-ray magnetic circular dichroism and electronic structure calculations, in order to determine the spin and orbital moments. The experimentally observed total spin moment, $M_s$, was found to be -0.24 $\pm$ 0.05~$\mu_B$ at 5~T. By comparison with the total moment of 0.16 $\pm$ 0.01~$\mu_B$, the orbital moment, $M_l$, was determined to be 0.40 $\pm$ 0.05~$\mu_B$. The U and Co spin moments were determined to be antiparallel. We find that the U 5\textit{f} electrons carry a spin moment of U$_s \approx$ -0.30~$\mu_B$ and that there is a Co spin moment of Co$_s \approx$ 0.06~$\mu_B$ induced via hybridization. The ratio U$_l/$U$_s$, of $-1.3 \pm 0.3$, shows the U moment to be itinerant. In order to ensure an accurate description of the properties of 5\textit{f} systems, and to provide a critical test of the theoretical approaches, it is clearly necessary to obtain experimental data for both the spin and orbital moments, rather than just the total magnetic moment. This can be achieved simply by measuring the spin moment with magnetic Compton scattering and comparing this to the total moment from bulk magnetization.