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We conduct a comprehensive study of three different magnetic semiconductors, CrI3, CrBr3, and CrCl3, by incorporating both few-layer and bilayer samples in van der Waals tunnel junctions. We find that the interlayer magnetic ordering, exchange gap, magnetic anisotropy, and magnon excitations evolve systematically with changing halogen atom. By fitting to a spin wave theory that accounts for nearest-neighbor exchange interactions, we are able to further determine a simple spin Hamiltonian describing all three systems. These results extend the 2D magnetism platform to Ising, Heisenberg, and XY spin classes in a single material family. Using magneto-optical measurements, we additionally demonstrate that ferromagnetism can be stabilized down to monolayer in more isotropic CrBr3, with transition temperature still close to that of the bulk. 

Electrical control on interfaces is one of the key approaches to harvest advanced functionalities in modern electronic devices. In this work, it is proposed and demonstrated that a “battery‐like” tunnel junction structure can be embedded with added control and functionalities via reversible lithium‐ion motion. In a model system of FeCo/FeCoO_x/LiF/FeCo magnetic tunnel junctions, the ultrathin LiF barrier makes strong electric fields possible under moderate applied voltages, and can therefore electrically drive reversible lithium‐ion migration within the barrier. The ion motion subsequently leads to reversible interfacial modifications that generates over a thousand percent resistance change across the devices. Meanwhile, sizable tunneling magnetoresistance persists and even reverses the sign of spin polarization as a function of the interfacial control. The devices are therefore responsive to both electric and magnetic field manipulations, giving rise to diverse and nonvolatile functionalities.