Ferromagnetism in van der Waals compound MnSb1.8Bi0.2Te4

MnBi2Te4 has recently been established as the first intrinsic antiferromagnetic (AFM) topological insulator. Although quantum anomalous Hall effect (QAHE) has been observed in MnBi2Te4, it is only realized with odd numbers of septuple layers due to the AFM interlayer coupling. Therefore, it is crucial to stabilize ferromagnetic (FM) phase in MnBi2Te4. We have discovered a new FM phase with the Curie temperature of 26 K in the MnSb1.8Bi0.2Te4 sample through tuning growth conditions, in contrast to the AFM order seen in the Mn(Bi1-xSbx)2Te4 family. We have investigated magnetotransport properties of the FM thin flakes and observed features similar to topological Hall effect. Our work pushes forward the realization of intrinsic FM topological insulator and establishes a new platform to explore novel topological quantum states arising from the interplay between magnetism and band topology.