Magnetic dilution effect and topological phase transitions in (Mn1−xPbx)Bi2Te4

We report, as the first intrinsic antiferromagnetic topological insulator, MnBi₂Te₄ has provided a material platform to realize various emergent phenomena arising from the interplay of magnetism and band topology. Here, by investigating (Mn_1-xPb_x)Bi₂Te₄(0 ≤ x ≤ 0.82) single crystals via the x-ray, electrical transport, magnetometry and neutron measurements, chemical analysis, external pressure, and first-principles calculations, we reveal the magnetic dilution effect on the magnetism and band topology in MnBi₂Te₄. With increasing x, both lattice parameters a and c expand linearly by around 2%. All samples undergo the paramagnetic to A-type antiferromagnetic transition with the Néel temperature decreasing lineally from 24 K at x = 0 to 2 K at x = 0.82. Our neutron data refinement of the x = 0.37 sample indicates that the ordered moment is 4.3(1)μ_B/Mn at 4.85 K and the amount of the Mn_Bi antisites is negligible within the error bars. Isothermal magnetization data reveal a slight decrease of the interlayer plane-plane antiferromagnetic exchange interaction and a monotonic decrease of the magnetic anisotropy due to diluting magnetic ions and enlarging the unit cell. For x = 0.37, the application of external pressures enhances the interlayer antiferromagnetic coupling, boosting the Néel temperature at a rate of 1.4 K/GPa and the saturation field at a rate of 1.8 T/GPa. 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.