Large‐Area Epitaxial Film Growth of van der Waals Ferromagnetic Ternary Chalcogenides

Abstract

non-vdW crystals (such as Mn 3 Si 2 Te 6, [12,13] ) has led to an interesting arena for studying fundamental 2D magnetism and provided numerous opportunities for 2D magnetic, magnetoelectric, and magnetooptic applications. [14,15] Electrical control of both charge and spin degrees of freedom in 2D ferromagnetic semiconductors is an important step in creating novel spintronic devices. As a single integrated platform, the spintronic devices based on these materials are expected to complement or outperform (in some cases) the conventional semiconductor-based devices. [16] However, compared to binary 2D metal chalcogenides, synthesis of ternary 2D metal chalcogenides is far more challenging, so the proof-of-concept studies on the magnetoelectric phenomena of the ferromagnetic ternary 2D metal chalcogenides have been performed on thin flakes mechanically exfoliated from bulk crystals. [9,17] There have been limited reports on the synthesis of ferromagnetic 2D ternary metal chalcogenide thin films. [18,19] The synthesis from pure elemental mixtures in an evacuated quartz ampule at 900-1100 °C through the self-flux of elements took 5-20 days. [7,13,17,20] Only two types of thin films have been synthesized via molecular beam epitaxy (MBE) in an ultra-high vacuum condition. [21][22][23] Very recently, a few CVD-based synthesis have been reported for binary 2D metal chalcogenide magnetic crystals such as CrSe and FeTe. [24,25] However, to the best of our knowledge, the conventional CVD-based and Following the first experimental realization of intrinsic ferromagnetism in 2D van der Waals (vdW) crystals, several ternary metal chalcogenides with unprecedented long-range ferromagnetic order have been explored. However, the synthesis of large-area 2D ternary metal chalcogenide thin films is a great challenge, and a generalized synthesis has not been demonstrated yet. Here, a quick and scalable synthesis of epitaxially aligned ferromagnetic ternary metal chalcogenide thin films (Cr 2 Ge 2 Te 6 , Cr 2 Si 2 Te 6 , Mn 3 Si 2 Te 6 ) is reported. The synthesis is based on the flux-controlled surface diffusion of Te on metal (Cr, Mn)-deposited wafer (Ge, Si) substrates. Magnetic anisotropy study of the epitaxial ternary thin films reveals the intrinsic magnetic easy axis; out-of-plane direction for Cr 2 Ge 2 Te 6 and Cr 2 Si 2 Te 6 , and in-plane direction for Mn 3 Si 2 Te 6 . In addition to the synthesis, this work creates an opportunity for transfer-free device fabrication for realizing magnetoelectronics based on the electrical control of both charge and spin degrees of freedom in 2D ferromagnetic semiconductors.

Composition‐Controllable Syntheses and Property Modulations from 2D Ferromagnetic Fe5Se8 to Metallic Fe3Se4 Nanosheets

“…The magnetic moments of Fe1, Fe2, and Fe3 are calculated as ≈0.88, 1.64, and 1.44 µB, respectively (Figure 6b). The average net magnetic moment of Fe 5 Se 8 is ≈1.30 µB, comparable to that of Cr 2 Si 2 Te 6 and Mn 3 Si 2 Te 6 (1.02 µB/Cr, 1.80 µB/Mn, respectively), [ 56 ] indicating the strong ferromagnetism in Fe 5 Se 8 . The FM ordering in Fe 5 Se 8 leads to the asymmetric density of states for the spin‐up and spin‐down components, as shown on the projected density of states, onto the three types of Fe atoms with the two spin components (Figure 6c).…”

Integrated Memory Devices Based on 2D Materials

“…Likewise, the foremost challenge for 2D spintronic IMDs is the preparation of large-area room-temperature vdW magnets. Although some studies have reported the wafer-scale growth of Fe 3 GeTe 2 and Cr 2 Ge 2 Te 6 , [175,176] their Curie temperatures are considerably below room temperature. Wang et al [177] first demon strated that the epitaxial growth of Fe 3 GeTe 2 on Bi 2 Te 3 could significantly increase the Curie temperature up to 400 K via interfacial exchange coupling.…”

Layer-Structured Anisotropic Metal Chalcogenides: Recent Advances in Synthesis, Modulation, and Applications

“…Copyright 2019, Rights Managed by Nature Publishing Group. (d, e) Reprinted with permission from ref . Copyright 2021 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.…”

“…The epitaxial relationship of the initial M x C y crystal domains with the substrate enabled unidirectional alignment of the synthesized thin film; hence, single-crystal thin film formation over the entire substrate was facilitated. In another study, Giri et al recently demonstrated the epitaxial wafer-scale thin film growth of 2D ferromagnetic ternary crystals, such as Cr 2 Ge 2 Te 6 , Cr 2 Si 2 Te 6 , Mn 3 Si 2 Te 6 , etc . The epitaxial growth was achieved by flux-controlled surface diffusion of Te into a Cr or Mn metal film that was predeposited on the conventional wafer substrates (Ge, Si).…”