Atomic-Layer-Controlled Magnetic Orders in MnBi 2 Te 4 -Bi 2 Te 3 Topological Heterostructures.

The natural van der Waals superlattice MnBi 2 Te 4 -(Bi 2 Te 3 ) m provides an optimal platform to combine topology and magnetism in one system with minimal structural disorder. Here, we show that this system can harbor both ferromagnetic (FM) and antiferromagnetic (AFM) orders and that these magnetic orders can be controlled in two different ways by either varying the Mn-Mn distance while keeping the Bi 2 Te 3 /MnBi 2 Te 4 ratio constant or vice versa. We achieve this by creating atomically engineered sandwich structures composed of Bi 2 Te 3 and MnBi 2 Te 4 layers. We show that the AFM order is exclusively determined by the Mn-Mn distance, whereas the FM order depends only on the overall Bi 2 Te 3 /MnBi 2 Te 4 ratio regardless of the distance between the MnBi 2 Te 4 layers. Our results shed light on the origins of the AFM and FM orders and provide insights into how to manipulate magnetic orders not only for the MnBi 2 Te 4 -Bi 2 Te 3 system but also for other magneto-topological materials.