Incommensurate magnetic order in Ag$_{2}$NiO$_{2}$

TL;DR

This study reveals incommensurate antiferromagnetic order in Ag$_{2}$NiO$_{2}$ below 56 K, with an additional transition at 22 K, using muon-spin-rotation spectroscopy to understand its magnetic properties.

Contribution

First demonstration of incommensurate magnetic order in Ag$_{2}$NiO$_{2}$ using $b5^+$SR, highlighting the magnetic behavior distinct from related compounds.

Findings

Incommensurate antiferromagnetic order below 56 K.

Additional magnetic transition at around 22 K.

Structural transition at approximately 260 K.

Abstract

The nature of the magnetic transition of the half-filled triangular antiferromagnet Ag$_{2}$NiO$_2$ with $T_{\rm N}$=56K was studied with positive muon-spin-rotation and relaxation ($\mu^+$SR) spectroscopy. Zero field $\mu^+$SR measurements indicate the existence of a static internal magnetic field at temperatures below $T_{\rm N}$. Two components with slightly different precession frequencies and wide internal-field distributions suggest the formation of an incommensurate antiferromagnetic order below 56 K. This implies that the antifrerromagnetic interaction is predominant in the NiO$_2$ plane in contrast to the case of the related compound NaNiO$_2$. An additional transition was found at $\sim$22 K by both $\mu^+$SR and susceptibility measurements. It was also clarified that the transition at $\sim$260 K observed in the susceptibility of Ag$_{2}$NiO$_{2}$ is induced by a purely structural transition.