Two-dimensional van der Waals multiferroic tunnel junctions for multi-state, low-power spintronics: A review

The convergence of spintronics and multiferroics has enabled unprecedented control of charge and spin degrees of freedom, opening new avenues for multifunctional tunnel junctions. This review provides a systematic overview of multiferroic materials and their integration into tunnel junction devices. First, we categorize multiferroics into type-I, type-II, and heterostructures, discussing synthesis strategies, material design, and approaches for tuning ferroic properties and magnetoelectric coupling. Next, we examine tunnel junctions, including magnetic and ferroelectric types, and focus on multiferroic tunnel junctions (MFTJs), highlighting the mechanisms underlying tunneling magnetoresistance (TMR) and tunneling electroresistance (TER), as well as the roles of interfacial engineering, electrode asymmetry, and multifield control. Special attention is given to emerging two-dimensional van der Waals MFTJs, which offer multi-level data storage, ultralow-power operation, and efficient spin filtering. Finally, we discuss challenges and future directions, emphasizing the importance of room-temperature, strongly coupled 2D multiferroics, scalable fabrication, and interface optimization for next-generation nonvolatile memory and multifunctional spintronic applications.