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MnBi2Te4/(Bi2Te3)n materials system has recently generated strong interest as a natural platform for realization of the quantum anomalous Hall (QAH) state. The system is magnetically much better ordered than substitutionally doped materials, however, the detrimental effects of certain disorders are becoming increasingly acknowledged. Here, from compiling structural, compositional, and magnetic metrics of disorder in ferromagnetic MnBi2Te4/(Bi2Te3)n it is found that migration of Mn between MnBi2Te4 septuple layers (SLs) and otherwise non-magnetic Bi2Te3 quintuple layers (QLs) has systemic consequences - it induces ferromagnetic coupling of Mn-depleted SLs with Mn-doped QLs, seen in ferromagnetic resonance as an acoustic and optical resonance mode of the two coupled spin subsystems. Even for a large SL separation (n ≳ 4 QLs) the structure cannot be considered as a stack of uncoupled two-dimensional layers. Angle-resolved photoemission spectroscopy and density functional theory studies show that Mn disorder within an SL causes delocalization of electron wave functions and a change of the surface band structure as compared to the ideal MnBi2Te4/(Bi2Te3)n. These findings highlight the critical importance of inter- and intra-SL disorder towards achieving new QAH platforms as well as exploring novel axion physics in intrinsic topological magnets.

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We explore the proximity effect between hexagonal boron nitride and two-dimensional magnets. A strong correlation between the optical emission from hBN and a magnetic phase transition in CrBr3 is found. Our approach demonstrates a novel method to locally apply magnetic fields and address selected defects.

Magnetic topological insulators are a new class of materials that combine magnetism with topology, which leads to exotic quantum phenomena such as the quantum anomalous Hall effect and the axion insulator phase. Of the magnetic topological insulators, those with MnBi2Te4 magnetic septuple layers self-assembled in a non-magnetic topological Bi2Te3 host material are of particular interest and have recently been extensively studied. Here, we present an overview of our recent advances in understanding the influence of several factors such as the ordering of Mn impurities, omnipresent magnetic disorder, and the position of the Fermi level on ferromagnetism and magnetotransport in such systems. In particular, the consequences of these effects for observation or lack of the quantized anomalous Hall effect are discussed. Both theoretical and experimental research on these issues is crucial for gaining controllable access to the quantum anomalous Hall effect and other spintronic phenomena, which have potential applications in low-power consumption electronic devices, data storage, and quantum computing.

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