Electrons in moiré flat band systems can spontaneously break time reversal symmetry, giving rise to a quantized anomalous Hall effect. Here we use a superconducting quantum interference device to image stray magnetic fields in twisted bilayer graphene aligned to hexagonal boron nitride. We find a magnetization of several Bohr magnetons per charge carrier, demonstrating that the magnetism is primarily orbital in nature. Our measurements reveal a large change in the magnetization as the chemical potential is swept across the quantum anomalous Hall gap consistent with the expected contribution of chiral edge states to the magnetization of an orbital Chern insulator. Mapping the spatial evolution of field-driven magnetic reversal, we find a series of reproducible micron scale domains pinned to structural disorder.

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Intrinsic large anomalous Hall effect (AHE) due to Berry curvature (BC) has attracted much attention in recent years not only for the fundamental research but also for the potential application prospect in sensors. Iron-based alloys are one of the representative materials. In this paper, the AHE has been studied in Fe3Ge alloys with DO19 and DO3 structures. Experimental results show that both of the samples have ferromagnetic properties with spontaneous moment of 5.51 and 5.29 μB/f.u. at 5 K for DO19 and DO3 Fe3Ge, respectively. The temperature dependence of longitudinal resistivity at a zero field makes clear that DO19 and DO3 Fe3Ge have a metal behavior. The value of anomalous Hall conductivity (AHC) for DO19 and DO3 polycrystalline Fe3Ge at room temperature is 175 and 106 S/cm, respectively. It is analyzed that AHC is mainly dominated by the intrinsic scattering associated with the BC. The band structures with and without spin–orbit coupling (SOC) indicates that the nodal line will gap out at the EF due to the perturbation of SOC in DO19 Fe3Ge, which induces a large BC in the sample, leading to a great AHC. In the DO3 structure, a degenerate band along the L–G path is split, producing an enhanced BC and AHC. Stable AHC up to room temperature makes Fe3Ge a promising candidate for the device of topological spintronics.

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