Very Large Tunneling Magnetoresistance in Layered Magnetic Semiconductor CrI$_3$

Abstract: Magnetic layered van der Waals crystals are an emerging class of materials giving access to new physical phenomena, as illustrated by the recent observation of 2D ferromagnetism in Cr2Ge2Te6 and CrI3. Of particular interest in semiconductors is the interplay between magnetism and transport, which has remained unexplored. Here we report first magneto-transport measurements on exfoliated CrI3 crystals. We find that tunneling conduction in the direction perpendicular to the crystalline planes exhibits a magnetoresistance as large as 10 000 %. The evolution of the magnetoresistance with magnetic field and temperature reveals that the phenomenon originates from multiple transitions to different magnetic states, whose possible microscopic nature is discussed on the basis of all existing experimental observations. This observed dependence of the conductance of a tunnel barrier on its magnetic state is a new phenomenon that demonstrates the presence of a strong coupling between transport and magnetism in magnetic van der Waals semiconductors.

• The paper demonstrates an unprecedented 10,000% magnetoresistance change in CrI3 through detailed magnetic field modulation.
• It identifies distinct magnetic state transitions in CrI3 via resistance and magneto-optical Kerr effect measurements.
• The research confirms low-temperature Fowler-Nordheim tunneling behavior, highlighting CrI3's potential in advanced spintronic devices.

Overview of Very Large Tunneling Magnetoresistance in Layered Magnetic Semiconductor CrI3

The paper under review presents comprehensive investigations into the tunneling magnetoresistance (TMR) of CrI3, a van der Waals magnetic semiconductor. The authors explore this recently realized material class with significant implications for condensed matter physics and potential applications in spintronic devices. The research reveals exceptionally large TMR in CrI3, on the order of 10,000%, emphasizing the strong correlation between magnetic states and electronic transport properties.

Key Findings

The primary results revolve around the novel observation of tunneling conduction in exfoliated CrI3 crystals. The conductivity is shown to vary dramatically based on magnetic field-induced transitions between different magnetic states within the material. This investigation not only confirms the occurrence of TMR in these materials but also quantifies its magnitude and response to both temperature and magnetic field variations.

1. Tunneling Magnetoresistance: The study precisely quantifies TMR, reporting a maximum magnitude change of about 10,000% as the magnetic field strength is varied. This is significant compared to non-magnetic materials where such large changes in resistance are uncommon.
2. Magnetic State Transitions: The research identifies multiple distinct magnetic states within CrI3, transitioning abruptly, and these are detected through signatures in both resistance measurements and magneto-optical Kerr effect (MOKE) observations.
3. Low-Temperature Tunneling: Below 20 K, transport is predominantly due to tunneling, evidenced by temperature-independent current-voltage characteristics confirming Fowler-Nordheim tunneling behavior.

Implications

The findings suggest robust coupling between magnetism and electron transport in CrI3, offering new avenues for exploring spintronic applications within two-dimensional van der Waals heterostructures. The notable TMR is indicative of CrI3's potential in devices that leverage tunneling processes manipulated by magnetic fields for novel functionalities, such as magnetic sensors or memory devices with high magnetic sensitivity.

Theoretical and Practical Considerations

Practical considerations involve the potential for integration into existing nanofabrication processes, though challenges remain in ensuring the stability of CrI3 under ambient conditions, which necessitates encapsulation strategies shown effective by the authors.

Theoretically, the paper pushes the boundary of understanding magnetic interactions in reduced dimensions. The observed TMR implies that the microscopic nature of magnetic domain transitions deserves further scrutiny, potentially offering illumination on quantum behavior that diverges from bulk analogs. The change in tunneling resistance as a function of magnetic state provides impetus for refined models of magnetotransport that account for complex coupling mechanisms.

Future Directions

Further research could extend beyond CrI3 to other magnetic van der Waals crystals, considering broader classes of magnetic states and thickness-dependent magnetic coupling caused by differing stacking orders or encapsulation materials. Investigations may also explore other conductive phenomena affected by magnetism, enhancing technological applications where modulation of electron transport by magnetic states can be exploited.

In conclusion, this paper signifies a pivotal step in uncovering and utilizing the unprecedented magnetoresistive properties of CrI3, contributing to the fundamental discourse on 2D magnetic materials and their potential exploitation in cutting-edge electronic and spintronic devices.