Incommensurate magnetic order in Ag${}_2$NiO${}_2$

Abstract

The nature of the magnetic transition of the half-filled triangular antiferromagnet Ag${}_2$NiO${}_2$ with $T_{\mathrm{N}}$=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 $T_{\mathrm{N}}$. 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.

6 pages, 6 figures, Phys. Rev. B 74, in press