Recent breakthroughs in two-dimensional van der Waals magnetic materials and emerging applications (original) (raw)
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Recent advances in two-dimensional van der Waals magnets
Microstructures, 2022
Two-dimensional (2D) magnets have evoked tremendous interest within the research community due to their fascinating features and novel mechanisms, as well as their potential applications in magnetic nanodevices. In this review, state-of-the-art research into the exploration of 2D magnets from the perspective of their magnetic interaction and order mechanisms is discussed. The properties of these magnets can be effectively modulated by varying the external parameters, such as the charge carrier doping, thickness effect, pressure and strain. The potential applications of heterostructures of these 2D magnets in terms of the interlayer coupling strength are reviewed, and the challenges and outlook for this field are proposed.
The Magnetic Genome of Two-Dimensional van der Waals Materials
ACS Nano
Magnetism in two-dimensional (2D) van der Waals (vdW) materials has recently emerged as one of the most promising areas in condensed matter research, with many exciting emerging properties and significant potential for applications ranging from topological magnonics to low-power spintronics, quantum computing, and optical communications. In the brief time after their discovery, 2D magnets have blossomed into a rich area for investigation, where fundamental concepts in magnetism are challenged by the behavior of spins that can develop at the single layer limit. However, much effort is still needed in multiple fronts before 2D magnets can be routinely used for practical implementations. In this comprehensive review, prominent authors with expertise in complementary fields of 2D magnetism (i.e., synthesis, device engineering, magneto-optics, imaging, transport, mechanics, spin excitations, and theory and simulations) have joined together to provide a genome of current knowledge and a guideline for future developments in 2D magnetic materials research.
Two‐Dimensional Magnets: Forgotten History and Recent Progress towards Spintronic Applications
Advanced Functional Materials, 2019
The recent discovery of 2D magnetic order in van der Waals materials has stimulated a renaissance in the field of atomically thin magnets. This has led to promising demonstrations of spintronic functionality such as tunneling magnetoresistance. The frantic pace of this emerging research, however, has also led to some confusion surrounding the underlying phenomena of phase transitions in 2D magnets. In fact, there is a rich history of experimental precedents beginning in the 1960s with quasi‐2D bulk magnets and progressing to the 1980s using atomically thin sheets of elemental metals. This review provides a holistic discussion of the current state of knowledge on the three distinct families of low‐dimensional magnets: quasi‐2D, ultrathin films, and van der Waals crystals. It highlights the unique opportunities presented by the latest implementation in van der Waals materials. By revisiting the fundamental insights from the field of low‐dimensional magnetism, this review highlights fa...
Prospects and Opportunities of 2D van der Waals Magnetic Systems
Annalen der Physik, 2020
The existence of spontaneous magnetization in low dimensional magnetic systems has attracted intensive studies since the early 60s and research remains very active even now. Only recently, magnetic van der Waals (vdW) systems down to a few layers have been broadly discussed for their magnetic order ground states at finite temperature. The naturally inherited layered structure of the vdW magnetic systems possessing onsite magnetic anisotropy from band electrons can suppress the long‐range fluctuations. This provides an excellent vehicle to study the transition of magnetism to 2D limits both theoretically and experimentally. Here the current status of 2D vdW magnetic system and its potential applications are briefly summarized and discussed.
A perspective on two-dimensional van der Waals opto-spin-caloritronics
Applied Physics Letters
Two-dimensional (2D) van der Waals magnetic semiconductors displaying controllable ferromagnetism at room temperature form atomically sharp interfaces with various substrates. Such heterostructures create platforms for understanding spin-dependent phenomena across interfaces and surfaces for high-performance technological applications. Combining these 2D magnets with light and the spin Seebeck effect (SSE) in state-of-the-art thermo-opto-spin studies forms a new paradigm in the field of spin-caloritronics that harnesses light as the new heat. In this Perspective, we detail how to exploit recent advances in 2D van der Waals materials to boost the SSE and propose a strategy for optically-controlled SSE in 2D magnetic semiconductor-based heterostructures with the intent to establish the research thrust of "opto-spin-caloritronics". Atomically thin van der Waals magnets and heterostructures are being tapped as the primary components of a next generation of computing devices based on spintronics or optospintronics. 1-3 In addition to their miniaturization, these two-dimensional (2D) magnets are expected to enable faster processing speeds, lower energy consumption, and even increased
Nano Letters, 2019
The family of 2D magnetic materials is continuously expanding because of the rapid discovery of exfoliable van der Waals magnetic systems. Recently, the synthesis of non-van der Waals magnetic "hematene" from common iron ore has opened an unconventional route to 2D material discovery. These non-van der Waals 2D systems are chemically stable and easily available and may have different or enhanced properties compared to their van der Waals counterparts. In this work, we have investigated and explained the nature of magnetic ordering in non-van der Waals 2D metal oxides. Two-dimensional hematene is found to be fully oxygen-passivated and stable under ambient conditions. It exhibits a striped ferrimagnetic ground state with a small net magnetic moment. Superexchange interactions are predicted to control the magnetic ground state of hematene, where pressure-induced spin crossover results in an observable net magnetic moment. Modulating the superexchange by alloying hematenes alters the magnetic ordering, tuning the system to a ferromagnetic ground state. Extending this strategy to the design of a new 2D material, we propose 2D chromia (α-Cr 2 O 3) or "chromene", which, because of larger inter-transition metal distances and suppressed AFM superexchange, has a ferromagnetic ground state. We also show that tuning the magnetic ordering in these materials controls the transport properties by modulating the band gap, which may be of use in spintronic or catalytic applications. T he discovery of magnetic 2D materials invites boundless possibilities for applications to quantum computation, spintronics, data storage, and other memory devices. 1,2 In this regard, the ingress of intrinsic 2D magnets in nanotechnology has provided a significant boost in the field of nanoscale devices. 3,4 The recent discovery of 2D layered magnets such as 2D chromium trihalides (CrI 3) has opened up opportunities for theoretical and experimental studies alike because of their fascinating fundamental physical properties and possible device applications. 5−8 These van der Waals magnetic insulators have shown the potential to form topological states or spintronic materials, as the isolation of few-layer ferromagnetic (FM) and antiferromagnetic (AFM) ground states have already been reported. 1,2,9,10 A new class of materials, transition-metal carbides and nitrides (MXenes), are solution-processed 2D sheets with wide chemical and structural diversity, leading to an exciting array of predicted magnetic properties. 11−13 Many 2D materials, such as graphene and transition-metal dichalcogenides (TMDs), remain intrinsically nonmagnetic when exfoliated from their 3D counterparts. 14 Doping, 15−18 defect formation, 19−21 and adatoms 22,23 are normally used to induce magnetism in these systems. However, control or switching of magnetic ordering in these systems remains a giant obstacle in the path of device applications because of the formation of metal clusters and disordered magnetic centers. 24 To find a way to circumvent these problems, one of the most abundant and inexpensive magnetic materials, iron, can play a crucial role. A recent experiment shows that the mined iron ore hematite (α-Fe 2 O 3) can be exfoliated to 2D hematene. 25 The bulk AFM structure of hematite converts to a weakly magnetic non-van der Waals material. 25 However, different plausible magnetic arrangements, different magnetic planes and phases in these systems, and the origin of magnetism remain unexplored. Similarly, 2D chromiteen (FeCr 2 O 4) has been shown to exhibit ferrimagnetic/ferromagnetic ordering depending upon the presence of defects or the surface structure. 26 Being non-van der Waals 2D monolayer materials, they can be etched in different atomic thicknesses and they do not require surface passivation because of the stable Fe−O bonds at the surface. This robustness under ambient conditions sets them apart from van der Waals 2D magnets such as CrI 3. This stable and abundant class of emerging 2D materials thus becomes the focal point of our study because of the possibility of exploring unconventional intrinsic magnetic behavior. We carry out a detailed density functional theory-based study to achieve a microscopic understanding of the magnetic behavior in non-van der Waals systems. We have studied the different planes and phases of hematene and primarily focus on the most stable exfoliated 001 plane of the material, which
Physical Review Materials, 2022
Two-dimensional (2D) van der Waals (vdW) magnetic materials have garnered considerable attention owing to the existence of magnetic order down to atomic dimensions and flexibility towards interface engineering, offering an attractive platform to explore novel spintronic phenomena and functionalities. Understanding of the magnetoresistive properties and their correlation to the underlying magnetic configurations is essential for 2D vdW-based spintronic or quantum information devices. Among the promising candidates, vdW ferromagnet (FM) Fe3GeTe2 shows an unusual magnetotransport behavior, tunable by doping at the magnetic (Fe) site, and tentatively arising from complicated underlying spin texture configurations. Here, we explore an alternative route towards manipulation of magnetotransport properties of a vdW FM without directly affecting the magnetic site i.e., by doping at the non-magnetic (Ge) site of Fe3(Ge,As)Te2. Interestingly, doping at the non-magnetic (Ge) site results in an unconventional Hall effect whose strength was considerably modified by increasing As concentration, possibly arising from emergent electromagnetic behavior from underlying complicated spin configurations. The present results provide a possible route to understand the intricate role played by the non-magnetic (Ge) atom towards magnetic properties of vdW FMs, and shows a novel direction towards tailoring of underlying interactions responsible for the stabilization of non trivial spin textures in 2D magnetic vdW materials.
2-D van der Waals Heterostructures
Two-dimensional van der Waals heterostructures (2D vdW HSs) can be constructed by stacking different 2D materials together in nearly endless ways, and have significantly enriched the 2D materials family. [40] Cornell researchers have become the first to control atomically thin magnets with an electric field, a breakthrough that provides a blueprint for producing exceptionally powerful and efficient data storage in computer chips, among other applications. [39] This "piezomagnetic" material changes its magnetic properties when put under mechanical strain. [38] Researchers have developed a new flexible sensor with high sensitivity that is designed to perform variety of chemical and biological analyses in very small spaces. [37]
Large-scale epitaxy of two-dimensional van der Waals room-temperature ferromagnet Fe5GeTe2
npj 2D Materials and Applications, 2022
In recent years, two-dimensional van der Waals materials have emerged as an important platform for the observation of long-range ferromagnetic order in atomically thin layers. Although heterostructures of such materials can be conceived to harness and couple a wide range of magneto-optical and magneto-electrical properties, technologically relevant applications require Curie temperatures at or above room temperature and the ability to grow films over large areas. Here we demonstrate the large-area growth of single-crystal ultrathin films of stoichiometric Fe 5 GeTe 2 on an insulating substrate using molecular beam epitaxy. Magnetic measurements show the persistence of soft ferromagnetism up to room temperature in 12 nm-thick films, with a Curie temperature of 293 K, and a weak out-of-plane magnetocrystalline anisotropy. The ferromagnetic order is preserved in bilayer Fe 5 GeTe 2 , with Curie temperature decreasing to 229 K. Surface, chemical, and structural characterizations confirm...