Element-specific insight into ferromagnetic stability in UCoGe revealed by soft x-ray magnetic circular dichroism
Abstract
We investigated the element-specific electronic states and magnetic properties of ferromagnetic superconductor UCoGe and Ru-substituted U(Co0.88Ru0.12)Ge using soft x-ray magnetic circular dichroism (XMCD) experiments at the absorption edges of U N4,5, Co L2,3, and Ge L2,3. YCoGe, a nonmagnetic compound without the 5f electrons, was also examined as a reference material.
The shapes of the XMCD spectra of UCoGe at the U N5 and Ge L2,3 edges are indistinguishably similar to those of U(Co0.88Ru0.12)Ge. On the other hand, the XMCD spectral shape at the Co L2 edge is very peculiar and is changed by the presence of the U 5f electrons and the Ru substitution.
From the sum rule analysis for the XMCD spectra, it was found that the magnetic moments of the U 5f and Co 3d electrons in UCoGe and U(Co0.88Ru0.12)Ge are aligned in the same direction under the present experimental conditions: T = 5.5-50 K and μ0H = 0-10 T. Furthermore, not only in UCoGe and U(Co0.88Ru0.12)Ge but even in the case of YCoGe, the Co 3d electrons have a large orbital magnetic moment, suggesting that the Co 3d electrons in these compounds are in a low-symmetry electronic environment originally.
Through the T and μ0H dependence of the XMCD intensity, it was revealed that the magnetic properties at the Co site are not simply induced by the magnetism at the U site and that the Co 3d electrons play an important role in the stability of ferromagnetism. The present findings clearly demonstrate that the contribution of not only the U 5f electrons but also the Co 3d electrons is very crucial to understanding the complex physical properties of the U(Co1-xRux)Ge system.