Tuning skyrmions in B20 compounds by 4d and 5d doping

TL;DR

This paper investigates how doping B20 compounds with 4d and 5d elements affects skyrmion stabilization, revealing enhanced magnetic interactions and predicting small skyrmions, with experimental synthesis confirming stability.

Contribution

It introduces a theoretical and experimental study on tuning skyrmions in B20 compounds through 4d and 5d doping, highlighting enhanced magnetic interactions and potential for small skyrmions.

Findings

Enhanced Dzyaloshinskii-Moriya interaction in 5d-doped compounds

Prediction of small skyrmions (~50 nm) in certain doped systems

Experimental synthesis confirms structural stability at high temperatures

Abstract

Skyrmion stabilization in novel magnetic systems with the B20 crystal structure is reported here, primarily based on theoretical results. The focus is on the effect of alloying on the 3d sublattice of the B20 structure by substitution of heavier 4d and 5d elements, with the ambition to tune the spin-orbit coupling and its influence on magnetic interactions. State-of-the-art methods based on density functional theory are used to calculate both isotropic and anisotropic exchange interactions. Significant enhancement of the Dzyaloshinskii-Moriya interaction is reported for 5d-doped FeSi and CoSi, accompanied by a large modification of the spin stiffness and spiralization. Micromagnetic simulations coupled to atomistic spin-dynamics and ab initio magnetic interactions reveal a helical ground state and field-induced skyrmions for all these systems. Especially small skyrmions $\sim$50 nm are predicted for Co$_{0.75}$Os$_{0.25}$Si, compared to $\sim$148 nm for Fe$_{0.75}$Co$_{0.25}$Si. Convex-hull analysis suggests that all B20 compounds considered here are structurally stable at elevated temperatures and should be possible to synthesize. This prediction is confirmed experimentally by synthesis and structural analysis of the Ru-doped CoSi systems discussed here, both in powder and in single-crystal forms.