Magnons and Spinons in $\mathrm{Ba}_2\mathrm{CoTeO}_6 $: A Composite System of Isolated Spin-$1/2$ Triangular Heisenberg-like and Frustrated Honeycomb Ising-like Antiferromagnets

TL;DR

This study investigates the magnetic orderings and excitations in Ba2CoTeO6, revealing independent subsystems with distinct magnetic behaviors and excitation spectra, including evidence of spinon excitations in the triangular Heisenberg-like subsystem.

Contribution

It provides the first detailed neutron scattering analysis of Ba2CoTeO6, demonstrating the coexistence of isolated spin-1/2 triangular and frustrated honeycomb antiferromagnetic subsystems with distinct excitations.

Findings

Subsystem A exhibits two magnon branches with roton-like minima and a spinon continuum.

Subsystem B's dispersion matches linear spin wave theory with third-neighbor interactions.

The two subsystems are magnetically independent and exhibit different ordering temperatures.

Abstract

We report the neutron scattering results on magnetic orderings and excitations in $\mathrm{Ba}_2\mathrm{CoTeO}_6$ composed of two almost isolated subsystems A and B, which are described as an $S\,{=}\,1/2$ triangular Heisenberg-like antiferromagnet and a frustrated honeycomb Ising-like antiferromagnet, respectively. Stripy ordering of subsystem B was confirmed below $T_{\rm N1}\,{=}\,12.0$ K, whereas sharp streaks were observed along $(1/3, 1/3, L)$ and $(2/3, 2/3, L)$ at 0.3 K (${\ll}\,T_{\rm N2}\,{=}\,3.0$ K). This indicates the two-dimensional nature of ordering in subsystem A. It was found that the excitation spectra of both subsystems are well separated and independent of each other. The excitation spectrum of subsystem A is composed of two single-magnon branches with roton-like minima at the M point and a clearly structured intense continuum, as similarly observed in $\mathrm{Ba}_3\mathrm{CoSb}_2\mathrm{O}_9$, which is strongly indicative of spinon excitations. Dispersion curves for subsystem B can be described by linear spin wave theory within the third-neighbor exchange interaction.