Magnetic dilution effect and topological phase transitions in (Mn_1-xPb_x)Bi₂Te₄

As the first intrinsic antiferromagnetic (AFM) topological insulator (TI), MnBi₂Te₄ has provided a material platform to realize various emergent phenomena arising from the interplay of magnetism and band topology, including quantum anomalous Hall effect. In this talk, I will present our investigation on (Mn_1-xPb_x)Bi₂Te₄ (0≤x≤0.82) single crystals that reveal the magnetic dilution effect on the magnetism and band topology in MnBi₂Te₄. With increasing x, Néel temperature decreases linearly while a slight decrease of the interlayer plane-plane antiferromagnetic exchange interaction and a monotonic decrease of the magnetic anisotropy are revealed. We attribute these observations to the dilution of magnetic ions and enlarging unit cell. The dilution of Mn atoms also leads to the decrease of the Mn_Bi antisites, reducing the magnetic inhomogenuity that is known to be detrimental to the realization of the quantum anomalous Hall effect. Furthermore, our first-principles calculations reveal that the band inversion in the two end materials, MnBi₂Te₄ and PbBi₂Te₄, occurs at the Γ and Z point, respectively, while two gapless points appear at x = 0.44 and x = 0.66, suggesting possible topological phase transitions with doping.