# Influence of cobalt substitution on the magnetism of NiBr$_2$

## TL;DR

This study investigates how cobalt substitution affects the structural and magnetic properties of NiBr$_2$, revealing a structural phase change and modifications in magnetic transitions across different cobalt concentrations.

## Contribution

It provides new insights into the structural and magnetic evolution of NiBr$_2$ with cobalt substitution, including a phase transition and magnetic phase diagram.

## Key findings

- Structural transition from CdCl$_2$ to CdI$_2$ type occurs between x=0.56 and 0.76.
- Magnetic transitions are altered by cobalt content, with incommensurate phase persisting up to x=0.56.
- Magnetic phase diagram summarizes the evolution of magnetic states with cobalt substitution.

## Abstract

Co substituted Ni$_{1-x}$Co$_x$Br$_2$ (0 $\leq~x~\leq$ 1) single crystals were synthesized using vapor transport. The physical properties of the crystals were characterized by x-ray powder diffraction, magnetization, and specific heat measurements. Room temperature x-ray powder diffraction data indicate a change from the CdCl$_2$ structure type to the CdI$_2$ structure type occurs within 0.56 $<~x~<$ 0.76. NiBr$_2$ has a commensurate antiferromagnetic phase below $T_{\rm N} \approx$ 46 K and an incommensurate magnetic ground state below $T_{\rm IC} \approx$ 20 K. Both magnetic transitions are affected by cobalt substitution, and the incommensurate phase transition is present up to at least $x$ = 0.56. The evolution of magnetism has been studied as a function of cobalt content and is summarized in the temperature-composition phase diagram.