- The paper demonstrates that applying up to 2 GPa pressure transforms CrI3 interlayer magnetism from antiferromagnetic to ferromagnetic coupling.
- It employs magnetic circular dichroism, electron tunneling, and Raman spectroscopy to verify a monoclinic-to-rhombohedral stacking transition.
- Results indicate potential for engineered spintronic applications by controlling 2D magnetic states through pressure-induced stacking modifications.
Pressure-Controlled Interlayer Magnetism in Atomically Thin CrI<sub\>3</sub>
The research paper explores the manipulation of interlayer magnetic states in atomically thin van der Waals magnetic insulator chromium triiodide (CrI<sub\>3</sub>) through the application of hydrostatic pressure. By applying pressure, the study investigates how the magnetic coupling between layers can be switched from antiferromagnetic (AF) to ferromagnetic (FM).
Key Findings and Methodology
The authors employed hydrostatic pressure up to 2 GPa, modifying the structural stacking order of CrI<sub\>3</sub> layers. The experimental investigation revealed an irreversible transition from interlayer antiferromagnetic to ferromagnetic coupling, documented through magnetic circular dichroism (MCD) and electron tunneling measurements. This transformation is attributed to a monoclinic to rhombohedral transition in stacking order, confirmed by polarized Raman spectroscopy.
Prior to this structural transition, the interlayer antiferromagnetic coupling energy was modifiable by pressure up to approximately 100%. Notably, the findings coincide with first principles calculations, suggesting that nanoscale magnetic textures might be engineered through moiré engineering. These results signify that stacking order is a decisive factor in dictating the magnetic ground state of atomically thin CrI<sub\>3</sub>.
Experimental Techniques
The researchers fabricated tunnel junctions with atomically thin CrI<sub\>3</sub> as the tunnel barrier, employing few-layer graphene as electrodes. The devices were encapsulated with hBN to mitigate environmental effects. Pressure's impact on magnetic characteristics was primarily tracked using tunneling magnetoresistance (TMR), alongside MCD microscopy and Raman spectroscopy.
Experiments observed a marked change in the MCD signal post-pressure application, indicating a potential AF-to-FM phase transition. This transition was further evaluated using MCD across various sample thicknesses. Pressure seemed to induce a monoclinic to rhombohedral change in the stacking order, which correlated with observed magnetic behavior alterations.
Implications and Future Directions
The study implications traverse both practical and theoretical realms. Practically, the ability to control interlayer magnetic states through pressure paves the way for advanced spintronic applications and provides insights into fabricating devices with tailored magnetic properties. Theoretically, the results contribute to a deeper understanding of thickness-dependent magnetic ground states in two-dimensional materials, thereby setting the stage for engineering novel magnetic phenomena such as moiré magnetism.
Future research could focus on refining the pressure conditions required for inducing complete structural phase transitions across various sample thicknesses. Additionally, further computational studies may provide quantitative comparisons to bridge experimental observations with theoretical predictions, especially concerning the pressure effects on interlayer exchange interactions.
This study serves as a significant step towards controlled magnetic manipulation in 2D materials, highlighting the potential of van der Waals heterostructures in next-generation technologies, presenting novel questions regarding the interplay between stacking order and emergent magnetic phenomena.