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Formation Mechanism of the Helical Q Structure in Gd-Based Skyrmion Materials

2020; American Physical Society; Volume: 125; Issue: 11 Linguagem: Inglês

10.1103/physrevlett.125.117204

1092-0145

Takuya Nomoto, Takashi Koretsune, Ryotaro Arita,

Rare-earth and actinide compounds

Using the ab initio local force method, we investigate the formation mechanism of the helical spin structure in ${\mathrm{GdRu}}_{2}{\mathrm{Si}}_{2}$ and ${\mathrm{Gd}}_{2}{\mathrm{PdSi}}_{3}$. We calculate the paramagnetic spin susceptibility and find that the Fermi surface nesting is not the origin of the incommensurate modulation, in contrast to the naive scenario based on the Ruderman-Kittel-Kasuya-Yosida mechanism. We then decompose the exchange interactions between the Gd spins into each orbital component, and show that spin-density-wave type interaction between the $\mathrm{Gd}\text{\ensuremath{-}}5d$ orbitals is ferromagnetic, but the interaction between the $\mathrm{Gd}\text{\ensuremath{-}}4f$ orbitals is antiferromagnetic. We conclude that the competition of these two interactions, namely, the interorbital frustration, stabilizes the finite-$\mathbit{Q}$ structure.