Although the investigation of 2DMMs is still at the primary stage, there have already been reported abundant ferromagnetic or antiferromagnetic ones, exhibiting quite different magnetic properties compared with their bulk counterparts. For instance, (1) owing to the ultrathin thickness, 2DMMs show strong quantum confinement and mechanical flexibility (2) 2DMMs possess good sensitivity and responsibility to defect engineering and external stimuli because the most atoms are exposed at the surface (3) 2DMMs can be artificially and flexibly integrated into various heterostructures on arbitrary substrates (4) 2DMMs also show many thickness-dependent, highly anisotropic, and multiphysical field tuning properties. Accordingly, 2DMMs possess a vast reservoir of properties that are greatly different from their bulk counterparts, including but not limited to the ones shown in Figure 1(a), which provide an ideal platform to explore the fundamental physics for the future application of 2DMM devices. In contrast to the conventional magnetic materials, the magnetic order of 2DMMs can persist down to the monolayer limit because of their great magnetic anisotropy. As for magnetism, intrinsic magnetic order in the monolayer/few-layer limit was firstly experimentally realized in 2D ferromagnets Cr 2Ge 2Te 6 and CrI 3 in 2017, after which various 2DMMs have been rapidly discovered and studied. Since the discovery of transport properties in graphene, new physical phenomena of 2D materials are being continuously revealed in a wide range of fields. Given that, it is highly desirable to discover and develop truly 2DMMs for novel magnetic properties and high-compacted devices. However, there remain a lot of challenges for these magnetic films with quasi-2D morphology: (1) the absence of intrinsic 2D crystal structure (2) the structural instability at the truly 2D scale (3) the vanishing of magnetic order in the ultrathin limit and (4) the requirement of good lattice matching with substrates and adjacent layers, and so forth. For instance, -zero ferromagnetism can be introduced into nonmagnetic films through strong interface coupling with magnetic materials. From that, many interesting physical phenomena and device configurations have emerged. At first, researchers have realized and investigated 2D magnetism in fabricating various magnetic films, such as transition metal oxides and magnetic alloys.
#2D THOMAS FERMI SCREENING FULL#
In particular, two-dimensional magnetic materials (2DMMs) have attracted enormous attention, owing to their merits for the simple integration of multiple-layered heterostructures and the full tunability by external electric fields. In the past decades, a rich variety of nanoscale magnetic materials have long been pursued by scientists. Magnetism has always been a classical and important subject for academic studies and application devices, to which low dimensionalities give new physical significance due to the strong quantum confinement effect. At last, we also provide our perspectives on the current challenges and future expectations in this field, which may be a helpful guide for theorists and experimentalists who are exploring the optical, electronic, and spintronic properties of 2DMMs. In the section of spintronic applications, we highlight spintronic devices based on 2DMMs, e.g., spin valves, spin-orbit torque, spin field-effect transistors, spin tunneling field-effect transistors, and spin-filter magnetic tunnel junctions. In the section of electronic properties, we raise several exciting phenomena in 2DMMs, i.e., long-distance magnon transport, field-effect transistors, varying magnetoresistance behavior, and (quantum) anomalous Hall effect. Then, particularly, we systematically summarize the recent work on the electronic and spintronic devices of 2DMMs. Afterwards, the optical probes in the light-matter-spin interactions at the 2D scale are discussed. Firstly, the microscopy characterization of the spatial arrangement of spins in 2D lattices is reviewed. Herein, we focus on the recent progress of 2DMMs and heterostructures in the aspects of their structural characteristics, physical properties, and spintronic applications. Since the first demonstration of truly two-dimensional magnetic materials (2DMMs) in 2017, a wide variety of magnetic phases and associated properties have been exhibited in these 2DMMs, which offer a new opportunity to manipulate the spin-based devices efficiently in the future. The emergence of low-dimensional nanomaterials has brought revolutionized development of magnetism, as the size effect can significantly influence the spin arrangement.
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