Resonant tender x-ray scattering from Ru-4d conduction electrons in the emergent inductor Gd3Ru4Al12

The spin and orbital texture of conducting electronic states in magnetic solids is a focus of intense scrutiny, being relevant to a multitude of emergent phenomena. These include novel optical responses, nonlinear transport properties, as well as spin current generation and control. Complex magnets with sizable local moments and intermediate spin-orbit coupling, e.g. in Ruthenium-based oxides and intermetallics, are believed to be suitable targets in this regard.
We studied the spiral ordering of Ruthenium spins, as driven by their interaction with local rare earth moments in centrosymmetric Gd3Ru4Al12. Resonant elastic scattering of tender x-rays was carried out at beamline P09 of the PETRA-III synchrotron at DESY in Hamburg, Germany. A specialized all-in vacuum beam path suppresses absorption of x-rays in air (E = 2.8-3 keV).
We exploit the resonant x-ray scattering process as an element-specific probe, targeting the spin texture of the Ru-4d electrons directly. Through comparison of scattering signals at the Ru-L2 and L3 absorption edges, we disentangle the spin and orbital textures in real space. Our analysis converges on a picture of a distorted spiral texture for Ru-4d, which results from a competition between Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions and spin-orbit coupling.
The experimental result is discussed in the framework of the Kondo Hamiltonian [1]. We highlight the relevance of our findings for the topological Hall effect in the field-induced skyrmion lattice phase of Gd3Ru4Al12 [2], and for the mechanism underlying the novel emergent (or quantum) inductance response in the spiral phase [3].

[1] M. Hirschberger et al., manuscript in preparation
[2] M. Hirschberger et al., Nature Communications 10, 5831 (2019)
[3] T. Yokouchi et al., Nature 586, 232–236 (2020)