Novel magnetic topological materials provide an ideal material platform to explore emergent phenomena such as quantized anomalous Hall effect (QAHE) and axion insulators etc. By rational design, we discover magnetic topological materials MnBi2nTe3n+1 (n>1), made of natural heterostructures with [MnBi2Te4] and [Bi2Te3] layers. Thermodynamic, transport, and neutron diffraction measurements show a gradual tuning of magnetism from antiferromagnetic to ferromagnetic with n. First-principles calculations and angle-resolved photoemission spectroscopy measurements reveal robust topological states with sizable surface hybridization gaps thus making MnBi2nTe3n+1 ideal candidate to realize QAHE. In reality, however, the consistent observation of QAHE with MnBi2nTe3n+1 is still met by various obstacles with fabrication and intrinsic crystal quality. In the second part of the talk, we investigate underlying reasons to the material aspect. We study the role of different defects in MnBi2Te4 and MnBi4Te7, controlled through different growth methods and Sb-doping respectively. These effects are manifested in magnetic, device transport and topological properties. The result shows fruitful tunability in magnetism and topology via defect control in the MnBi2nTe3n+1 family and provides fundamental understandings that pave ways to QAHE realization and relevant technological advances.