# Long period helical structures and twist-grain boundary phases induced by non magnetic ion doping in Mn$_{1-x}$(Co,Rh)$_{x}$Ge chiral magnet

## TL;DR

This study investigates how doping MnGe with non-magnetic Co and Rh ions alters its helical magnetic structures, leading to long-period helices and twist-grain boundary phases with complex dislocation textures.

## Contribution

It reveals the emergence of long-period helices and twist-grain boundary phases in doped MnGe, introducing a new understanding of magnetic dislocation textures in chiral magnets.

## Key findings

- Long-period helical magnetic structures observed at high doping levels.
- Double periodicity in neutron scattering spectra indicating complex phases.
- Presence of dense networks of screw dislocations with non-radial double-core skyrmions.

## Abstract

We study the evolution of helical magnetism in MnGe chiral magnet upon partial substitution of Mn for non magnetic 3d-Co and 4d-Rh ions. At high doping levels, we observe spin helices with very long periods -more than ten times larger than in the pure compound- and sizable ordered moments. This behavior calls for a change in the energy balance of interactions leading to the stabilization of the observed magnetic structures. Strikingly, neutron scattering unambiguously shows a double periodicity in the observed spectra at $x \gtrsim 0.45$ and $\gtrsim 0.25$ for Co- and Rh-doping, respectively. In analogy with observations made in cholesteric liquid crystals, we suggest that it reveals the presence of magnetic twist-grain-boundary phases, involving a dense short-range correlated network of screw dislocations. The dislocation cores are described as smooth textures made of non-radial double-core skyrmions.