Growth and characterization of the dynamical axion insulator candidateMn2Bi2Te5with intrinsic antiferromagnetism

Intrinsic antiferromagnetic ${\mathrm{Mn}}_{2}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{5}$ crystals, a candidate of dynamical axion insulator proposed theoretically recently, were successfully grown by the self-flux method. The crystal structure and chemical composition of ${\mathrm{Mn}}_{2}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{5}$ crystals were experimentally substantiated. Temperature-dependent resistivity of ${\mathrm{Mn}}_{2}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{5}$ shows a metallic behavior $(d\ensuremath{\rho}/dT>0)$ when temperature $T>25\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ and a subsequently semiconductorlike feature $(d\ensuremath{\rho}/dT<0)$. Magnetic measurement verifies that ${\mathrm{Mn}}_{2}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{5}$ is ferromagnetic at $ab$ plane but antiferromagnetic along the $c$ axis, whose N\'eel temperature is around 20 K. Analysis of magnetic hysteresis loops measured at different temperatures substantiates that critical indices of magnetic-paramagnetic phase transition in ${\mathrm{Mn}}_{2}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{5}$ are satisfied to the prediction of Landau mean-field theory. When $T<20\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, there are unconventional Hall effects, including both anomalous Hall effect and topological Hall effect, when magnetic field $B<3.4\phantom{\rule{0.16em}{0ex}}\mathrm{T}$. Based on theoretical electronic-band structure of ${\mathrm{Mn}}_{2}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{5}$, the anomalous Hall effect of ${\mathrm{Mn}}_{2}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{5}$ can be described by the Karplus-Luttinger (Berry curvature) mechanism, while the topological Hall effect of ${\mathrm{Mn}}_{2}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{5}$, under $B<3.4\phantom{\rule{0.16em}{0ex}}\mathrm{T}$, is attributed to noncollinear spin structure. Our results strongly suggest that ${\mathrm{Mn}}_{2}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{5}$ is an axion insulator.