Magnetic tunneling junctions based on 2D CrI3 and CrBr3: spin-filtering effects and high tunnel magnetoresistance via energy band difference

Recently, the study of two-dimensional materials has expanded to the field of spintronics. Intrinsically ferromagnetic van der Waals materials such as CrI3 and CrBr3 have received much attention due to their nearly 100% spin polarization and good stability, resulting in excellent performance in magnetic tunnel junctions. In this work, we design magnetic tunnel junctions (MTJs) of Cu/CrI3/Cu and Cu/CrBr3/Cu with electrodes of Cu(111) and a tunneling barrier of four-monolayer CrI3 or CrBr3. Our first-principle calculations combined with non-equilibrium Green's function method indicate that the CrBr3-based MTJ has a larger maximum tunneling magnetoresistance ratio than the CrI3-based MTJ. In a wide bias voltage range, the CrI3-based MTJ can maintain high spin-filtering performance, while that of the CrBr3-based MTJ degrades sharply as the bias voltage increases. It is noted that a negative differential resistance effect is observed in the CrBr3-based MTJ. The differences in spin transport properties between the CrI3-based MTJ and the CrBr3-based MTJ are clarified in terms of the physics inside the device, including the spin-dependent density of states, band structures, Bloch states, and the electron density difference. This work provides some physical insights for the design of 2D van der Waals MTJs.