Magnetic phase diagram in the three-dimensional triangular-lattice antiferromagnet Sr3CoTa2O9 with small easy-axis anisotropy

Abstract

We report the results of low-temperature magnetization and specific heat measurements of ${\mathrm{Sr}}_{3}{\mathrm{CoTa}}_{2}{\mathrm{O}}_{9}$ powder, in which ${\mathrm{Co}}^{2+}$ ions with effective spin-1/2 form a uniform triangular lattice in the $ab$ plane. It was found that ${\mathrm{Sr}}_{3}{\mathrm{CoTa}}_{2}{\mathrm{O}}_{9}$ undergoes successive antiferromagnetic transitions at ${T}_{\mathrm{N}1}=0.97\phantom{\rule{4pt}{0ex}}\mathrm{K}$ and ${T}_{\mathrm{N}2}=0.79\phantom{\rule{4pt}{0ex}}\mathrm{K}$ at zero magnetic field. As the magnetic field increases, both ${T}_{\mathrm{N}1}$ and ${T}_{\mathrm{N}2}$ decrease monotonically. The obtained magnetic field vs temperature phase diagram together with a sharp magnetization anomaly at a saturation field of ${\ensuremath{\mu}}_{0}{H}_{\mathrm{s}}=2.3$ T indicates that ${\mathrm{Sr}}_{3}{\mathrm{CoTa}}_{2}{\mathrm{O}}_{9}$ is described as a spin-1/2 three-dimensional triangular-lattice antiferromagnet with a weak easy-axis anisotropy. We discuss the characteristics of the magnetic phase diagram, which approximates the phase diagram for the magnetic field perpendicular to the $c$ axis.