Anisotropic spin-flip-induced multiferroic behavior in kagome Cu3Bi(SeO3)(2)O2Cl

Compared to the previous report on $\mathrm{C}{\mathrm{u}}_{3}\mathrm{Bi}{(\mathrm{Se}{\mathrm{O}}_{3})}_{2}{\mathrm{O}}_{2}X\phantom{\rule{0.16em}{0ex}}(X=\mathrm{Cl},\mathrm{Br})$ [V. Gnezdilov et al., (arXiv:1604.04249)],where no dielectric anomaly was observed without magnetic field near ${T}_{N}\ensuremath{\sim}25.6\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, we further present the dielectric behaviors without and with magnetic field in $\mathrm{C}{\mathrm{u}}_{3}\mathrm{Bi}{(\mathrm{Se}{\mathrm{O}}_{3})}_{2}{\mathrm{O}}_{2}\mathrm{Cl}$. At zero field $H=0$, an antiferromagnetic transition from magnetization and specific heat measurements is clearly established at ${T}_{N}$, while no dielectric anomaly was observed. Those results are similar to the previous report [V. Gnezdilov et al., (arXiv:1604.04249)]. Above the critical field ${H}_{\mathrm{c}}\ensuremath{\sim}0.8\phantom{\rule{0.16em}{0ex}}\mathrm{T}$, a metamagnetic spin-flip transition from antiferromagnetic to ferrimagnetic order at $T\ensuremath{\sim}{T}_{N}$ is induced anisotropically only for $H\ensuremath{\parallel}c$. Meanwhile, a ferroelectric behavior from dielectric and pyroelectric current measurements is observed below $T\ensuremath{\sim}{T}_{N}$; then a corresponding type-II multiferroics emerges above ${H}_{\mathrm{c}}$. The key mechanism of the anisotropic spin-flip-induced multiferroicity in $\mathrm{C}{\mathrm{u}}_{3}\mathrm{Bi}{(\mathrm{Se}{\mathrm{O}}_{3})}_{2}{\mathrm{O}}_{2}\mathrm{Cl}$ can be ascribed to the breaking of magnetic twofold symmetry in the $bc$ plane above ${H}_{\mathrm{c}}$.