Multiferroic heterojunctions: 1 + 1 ≠ 2

Multiferroicity or magnetoelectric coupling that occurs in composite materials is realized through interfaces of the heterostructures. It is essentially a so-called emergent phenomenon, which is not exhibited in either of the heterostructure constituents alone. This represents a kind of sudden leap process in the evolution from simple to complex material systems, i.e. 1 + 1 ≠ 2. This paper focuses on recent studies of multiferroic heterojunctions, including interface magnetoelectric effects, multiferroic tunnel junctions, and electric-field control of magnetism based on heterostructures. These achievements suggest that heterostructures might represent a breakthrough for practical applications utilizing multiferroicity. (authors)