Molecular beam epitaxy used to realize tailorable magnetic van der Waals insulator

Magnetic van der Waals materials are stacks of magnetic monolayer crystals that adhere due to noncovalent electric forces, and are becoming an emerging type of material for spintronics and related fields. As an example, spintronics utilizes the spin of electrons to store or process information as a solid-state device. The challenge is that these magnetic van der Waals materials lack customization since they are typically exfoliated from larger bulk crystals or grown using chemical deposition techniques.

In new research by Mogi et al., the authors created stacks of van der Waals materials with differing properties using molecular beam epitaxy, a technique which allows precise control of the elemental ratios and thicknesses of the created films. The atomic concentrations of the incident molecular beams were fine-tuned to achieve high-quality films with the optimal elemental compositions and the desired phase. Specific combinations of these layers opens avenues for new types of materials and devices.

The team grew a van der Waals ferromagnetic insulator, an insulator with magnetic properties, directly on a topological insulator, which only conducts along its surface, using molecular beam epitaxy. The van der Waals layer exhibits bulklike magnetic ordering temperature and perpendicular magnetic anisotropy, even in films with extremely small thicknesses. This special heterostructure may allow manipulation of the surface of the topological insulator from the coupling between the two materials.

The study shows promise in designing and realizing new properties for spintronics applications, as well as advancing other areas involving functional interfaces. Creating these heterostructures with molecular beam epitaxy is a significant step forward for novel spintronic devices utilizing 2-D materials and topological insulators.

Source: “Ferromagnetic insulator Cr₂Ge₂Te₆ thin films with perpendicular remanence,” by M. Mogi, A. Tsukazaki, Y. Kaneko, R. Yoshimi, K. S. Takahashi, M. Kawasaki, and Y. Tokura, APL Materials (2018). The article can be accessed at https://doi.org/10.1063/1.5046166 .