# Incommensurate magnetism in K$_2$MnS$_{2-x}$Se$_x$ and prospects for tunable frustration in a triangular lattice of pseudo-1D spin chains

## TL;DR

This study investigates the magnetic properties of K$_2$MnS$_{2-x}$Se$_x$ compounds, revealing incommensurate cycloid magnetic structures and highlighting their potential for tuning magnetic frustration in a pseudo-1D triangular lattice.

## Contribution

It provides the first detailed analysis of magnetic structures in K$_2$MnS$_2$, K$_2$MnSe$_2$, and their solid solutions, demonstrating persistent incommensurate magnetism despite structural changes.

## Key findings

- Incommensurate cycloid magnetic structure with k = [0.58 0 1] observed across all samples.
- Magnetic ordering remains robust despite a 12% increase in cell volume.
- Geometric frustration leads to incommensurability and a two-step magnetic transition.

## Abstract

We report the first detailed investigation of K$_2$MnS$_2$ and K$_2$MnSe$_2$ from the K$_2$MnS$_2$ structure type and their magnetic solid solution K$_2$MnS$_{2-x}$Se$_x$ and find that compounds of this structure type consist of strongly-coupled pseudo-one-dimensional antiferromagnetic chains that collectively represent a frustrated two-dimensional triangular antiferromagnet. Bulk samples of K$_2$MnS$_{2-x}$Se$_x$ with $0 \leq x \leq 2$ are characterized using X-ray diffraction, neutron diffraction, magnetization and heat capacity measurements. An incommensurate cycloid magnetic structure with a magnetic propagation vector $k = [0.58~0~1]$ is observed for all samples in K$_2$MnS$_{2-x}$Se$_x$, and the ordering is robust despite a 12\% increase in cell volume. Geometric frustration of chains results in incommensurability along $a$ and a two-step magnetic transition. The varying geometries accessible in compounds of this structure type are presented as promising avenues to tune frustration.