Magnetization Process and Collective Excitations in the S=1/2 Triangular-Lattice Heisenberg Antiferromagnet Ba3CoSb2O9

TL;DR

This study investigates the magnetic properties and collective excitations of Ba3CoSb2O9, a model 2D S=1/2 triangular-lattice antiferromagnet, revealing detailed magnetization behavior, anisotropy, and field-induced transitions through experiments and theoretical analysis.

Contribution

It provides comprehensive experimental data and theoretical insights into the magnetization process and collective excitations in Ba3CoSb2O9, highlighting anisotropy and additional field-induced transitions.

Findings

Magnetization curve matches theoretical models except near 3/5 M_s

An anomaly near 3/5 M_s suggests a field-induced transition

Weak easy-plane anisotropy is evidenced by ESR and magnetization data

Abstract

We have performed high-field magnetization and ESR measurements on Ba$_3$CoSb$_2$O$_9$ single crystals, as a representative two-dimensional spin-1/2 Heisenberg antiferromagnet on a uniform triangular lattice, and have determined all the magnetic parameters. For an applied magnetic field $H$ parallel to the $ab$-plane, the entire magnetization curve including the plateau at one-third of the saturation magnetization ($M_\mathrm{s}$) is in excellent agreement with the results of theoretical calculations except an anomaly near $(3/5)M_\mathrm{s}$, indicative of an additional field-induced transition. However, for $H\,{\parallel}\,c$, the magnetization curve exhibits a cusp near $M_\mathrm{s}/3$. Paramagnetic resonance signals above the N\'eel temperature indicate the nearly isotropic $g$-factor. A detailed analysis of the collective ESR modes observed in the ordered state, combined with the magnetization process, provides evidence of the weak easy-plane anisotropy.