Growth and characterization of the dynamical axion insulator candidate Mn₂Bi₂Te₅ with intrinsic antiferromagnetism

Intrinsic antiferromagnetic Mn2Bi2Te5 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 Mn2Bi2Te5 crystals were experimentally substantiated. Temperature-dependent resistivity of Mn2Bi2Te5 shows a metallic behavior (d./dT > 0) when temperature T > 25 K and a subsequently semiconductorlike feature (d./dT < 0). Magnetic measurement verifies that Mn2Bi2Te5 is ferromagnetic at ab plane but antiferromagnetic along the c axis, whose Neel temperature is around 20 K. Analysis of magnetic hysteresis loops measured at different temperatures substantiates that critical indices of magnetic-paramagnetic phase transition in Mn2Bi2Te5 are satisfied to the prediction of Landau mean-field theory. When T < 20K, there are unconventional Hall effects, including both anomalous Hall effect and topological Hall effect, when magnetic field B < 3.4 T. Based on theoretical electronic-band structure of Mn2Bi2Te5, the anomalous Hall effect of Mn2Bi2Te5 can be described by the Karplus-Luttinger (Berry curvature) mechanism, while the topological Hall effect of Mn2Bi2Te5, under B < 3.4 T, is attributed to noncollinear spin structure. Our results strongly suggest that Mn2Bi2Te5 is an axion insulator.