The Effects of Cobalt Doping on the Skyrmion Hosting Material Cu$_2$OSeO$_3$

TL;DR

This study investigates how cobalt doping influences the atomic and magnetic structures of Cu$_2$OSeO$_3$, revealing modifications in magnetic ordering, skyrmion stability, and phase transition temperatures through comprehensive experimental analysis.

Contribution

It provides new insights into the effects of Co$^{2+}$ doping on the magnetic phases and skyrmion properties of Cu$_2$OSeO$_3$, including synthesis, structural, and magnetic characterization.

Findings

Co doping expands the unit cell without changing bond lengths.

Magnetic ordering is significantly altered by Co incorporation.

Doping stabilizes skyrmion lattices over a broader temperature range.

Abstract

Cu$_2$OSeO$_3$ has fascinating magnetic phases that can be easily manipulated through chemical doping. In this work, we report on the synthesis and characterization of Co-doped Cu$_2$OSeO$_3$ and its influence on both the atomic and magnetic structure. Polycrystalline (Cu$_{1_-x}$Co$_x$)$_2$OSeO$_3$ samples with 0 < x < 0.1 were synthesized and the presence of Co was confirmed via elemental analysis. Using synchrotron powder X-ray diffraction, and high-resolution neutron powder diffraction, the incorporation of Co$^{2+}$ into the Cu2 sites was confirmed. Co-doping led to an expansion to the unit cell but shows no apparent changes in bond lengths and angles in the crystal structure. Magnetization measurements showed that the incorporation of Co$^{2+}$ into the Cu2 site led to significant changes to the magnetic ordering of the material. Including an increase to the critical fields, the lowering of the critical temperature of the helimagnetic phase, and both a lowering and expansion of the skyrmion pocket temperatures. Lastly, small-angle neutron scattering was used to probe the magnetic structures hosted by the material. It was found that upon doping, the skyrmion lattice nucleates at lower temperatures as well as stabilized over a large temperature range. The observed results highlight the effects of incorporating a magnetic ion into the crystal structure and how it affects the internal magnetic structures.