Coexistence of ferromagnetism and topology by charge carrier engineering in the intrinsic magnetic topological insulator Mn Bi4Te7

Intrinsic magnetic topological insulators (MTIs) Mn Bi₂Te₄ and Mn Bi₂Te₄/(Bi_{2Te3) n} are expected to realize the high-temperature quantum anomalous Hall effect and dissipationless electrical transport. However, there is still a lack of ideal MTI candidates with magnetic ordering of the ferromagnetic (FM) ground state. Here, we show a MTI sample of Mn (Bi_{0.7Sb0.3) 4}Te₇ which holds the coexistence of a FM behavior state and topological nontriviality. The dramatic modulation of the magnetism is induced by a charge carrier engineering process via the Sb substitution in the Mn Bi₄Te₇ matrix with antiferromagnetic ordering. The evolution of magnetism in Mn (Bi_{1−xSbx) 4}Te₇ is systematically investigated by our magnetic measurements and theoretical calculations. The clear topological surface states of the FM sample of Mn (Bi_{0.7Sb0.3) 4}Te₇ are further verified by angle-resolved photoemission spectroscopy. The demonstration of the intrinsic FM-MTI of Mn (Bi_{0.7Sb0.3) 4}Te₇ in this paper sheds light on further material optimization of intrinsic MTIs and paves the way for further studies to clarify the relationships between topology, magnetism, and charge carriers in topological materials.