Increasing the skyrmion stability in Cu$_2$OSeO$_3$ by chemical substitution

TL;DR

This study demonstrates that chemical substitution with Ni or Zn in Cu$_2$OSeO$_3$ can respectively enhance or weaken the Dzyaloshinskii-Moriya interaction, thereby tuning the stability and properties of skyrmions in this insulating helimagnet.

Contribution

The paper provides experimental evidence on how chemical substitution affects DMI and skyrmion stability in Cu$_2$OSeO$_3$, a key insight for magnetic material engineering.

Findings

Ni substitution enhances DMI and skyrmion stability.

Zn substitution weakens DMI and reduces skyrmion stability.

Changes in DMI correlate with spin-spiral wavevector and temperature range.

Abstract

The cubic chiral helimagnets with the $P2_13$ space group represent a group of compounds in which the stable skyrmion-lattice state is experimentally observed. The key parameter that controls the energy landscape of such systems and determines the emergence of a topologically nontrivial magnetic structures is the Dzyaloshinskii-Moriya interaction (DMI). Chemical substitution is recognized as a convenient instrument to tune the DMI in real materials and has been successfully utilized in studies of a number of chiral magnets, such as MnSi, FeGe, MnGe, and others. In our study, we applied small-angle neutron scattering to investigate how chemical substitution influences the skyrmionic properties of an insulating helimagnet Cu$_2$OSeO$_3$ when Cu ions are replaced by either Zn or Ni. Our results demonstrate that the DMI is enhanced in the Ni-substituted compounds (Cu,Ni)$_2$OSeO$_3$, but weakened in (Cu,Zn)$_2$OSeO$_3$. The observed changes in the DMI strength are reflected in the magnitude of the spin-spiral propagation vector and the temperature stability of the skyrmion phase.