Magnetic tunnel junctions (MTJs) serve as essential platforms for investigating spin transport properties, magnetic phase transitions, and anisotropy in magnetic materials. Recently two-dimensional van der Waals antiferromagnetic insulators like chromium chloride (CrCl₃) or chromium iodide (CrI₃) have been used to develop spin-filtering magnetic tunnel junctions (sf-MTJs), improving the device performance for material property exploration and spintronic applications. However, it is crucial to recognize that the spin-filtering effect is not the sole determining factor of tunneling magnetoresistance (TMR) in these junctions; the interface magnetic exchange interactions and adjustable electrode density of states (DOS) fluctuations, response to applied electric or magnetic fields, can also influence the tunneling current.

In this study, we fabricate MTJ devices by using mechanically-exfoliated few-layer CrCl₃ as the tunnel barrier and few-layer graphene (FLG) as electrodes through dry transfer technique. Conducting low-temperature quantum transport measurements, we observe unconventional TMR behaviors, including bias-voltage-dependent TMR, oscillatory tunneling current under high magnetic fields, and tunable tunneling current via gate voltage.

A qualitative model of elastic tunneling current is employed to analyze the spin and band characteristics of the MTJ device. The observed bias-voltage-dependent TMR is attributed to the changes in the tunneling mechanism due to magnetic proximity effect, which induces magnetization in the FLG electrode near the FLG/CrCl₃ interface. The antiparallel alignment of polarized spin to CrCl₃’s magnetization results in injected charge carriers facing a higher tunnel barrier, leading to negative TMR at lower bias voltages. As the bias voltage increases, the magnetic proximity effect lessens, and the device reverts to its conventional spin-filtering functionality. The oscillatory tunneling current is explained by the graphene electrode’s quantum oscillatory density of states behavior under vertical magnetic fields, which can be controlled by the applied gate voltage.

This study contributes to the understanding of previously unexplored TMR phenomena in two-dimensional MTJs, deepening our insights into carrier transport properties in these heterostructures and broadening avenues for investigating the physical properties of two-dimensional magnetic materials and their spintronic applications.