# Theoretical and experimental study of high-pressure synthesized B20-type compounds Mn$_{1-x}$(Co,Rh)$_x$Ge

## TL;DR

This study combines experimental and ab initio methods to investigate high-pressure synthesized Mn$_{1-x}$(Co,Rh)$_x$Ge compounds, revealing how substitution affects magnetic phases and structure stability at normal conditions.

## Contribution

It provides a detailed magnetic phase diagram and compares the effects of 3d and 4d element substitution on magnetic properties and structure.

## Key findings

- Both systems show composition-dependent helical magnetic order.
- Mn$_{1-x}$Co$_x$Ge exhibits coexistence of two helices in certain regions.
- High-pressure phases remain metastable with preserved B20 structure.

## Abstract

The search and exploration of new materials not found in nature is one of modern trends in pure and applied chemistry. In the present work, we report on experimental and \textit{ab initio} density-functional study of the high-pressure-synthesized series of compounds Mn$_{1-x}$(Co,Rh)$_x$Ge. These high-pressure phases remain metastable at normal conditions, therewith they preserve their inherent noncentrosymmetric B20-type structure and chiral magnetism. Of particular interest in these two isovalent systems is the comparative analysis of the effect of $3d$ (Co) and $4d$ (Rh) substitution for Mn, since the $3d$ orbitals are characterized by higher localization and electron interaction than the $4d$ orbitals. The behavior of Mn$_{1-x}$(Co,Rh)$_x$Ge systems is traced as the concentration changes in the range $0 \leq x \leq 1$. We applied a sensitive experimental and theoretical technique which allowed to refine the shape of the temperature dependencies of magnetic susceptibility $\chi(T)$ and thereby provide a new and detailed magnetic phase diagram of Mn$_{1-x}$Co$_x$Ge. It is shown that both systems exhibit a helical magnetic ordering that very strongly depends on the composition $x$. However, the phase diagram of Mn$_{1-x}$Co$_x$Ge differs from that of Mn$_{1-x}$Rh$_x$Ge in that it is characterized by coexistence of two helices in particular regions of concentrations and temperatures.