Two‐Dimensional Magnets: Forgotten History and Recent Progress towards Spintronic Applications

Abstract

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 factors that can be used to enhance material performance. For example, the limits imposed on the critical temperature by the Mermin-Wagner theorem can be escaped in three separate ways: magnetocrystalline anisotropy, long-range interactions, and shape anisotropy. Several recent experimental reports of atomically thin magnets with Curie temperatures above room temperature are highlighted.

Critical behavior of intercalated quasi-van der Waals ferromagnet Fe0.26TaS2

“…This conclusion is consistent with our previous analysis. Long-range interaction and magnetocrystalline anisotropy are two strategies for a magnet to be exempt from the Mermin-Wagner theorem [53]. The bulk 3D ferromagnet FTS evidently owns these two features.…”

Proximity Spin–Orbit Torque on a Two-Dimensional Magnet within van der Waals Heterostructure: Current-Driven Antiferromagnet-to-Ferromagnet Reversible Nonequilibrium Phase Transition in Bilayer CrI3

“…Introduction.-The recent discovery of twodimensional (2D) magnets derived from layered van der Waals (vdW) materials [1,2] has opened new avenues for basic research on low-dimensional magnetism [3,4] and potential applications in spintronics [5][6][7][8][9]. Their magnetic phases can substantially differ from those in conventional bulk magnetic materials due to large structural anisotropy which makes possible different sign and magnitude of intralayer J intra and interlayer J inter exchange coupling between localized magnetic moments.…”

Giant anisotropy of Gilbert damping in a Rashba honeycomb antiferromagnet

“…As we will show below, the presence of spinorbit interaction does not only provide us with a finite α n but also drastically change the symmetry structure of Eqs. (8). We will demonstrate that the onset of spin-orbit interaction strongly affects the coupling of the localized spin subsystem to the electron bath (described by the tight-binding model) resulting in a strong reduction in the ability of conduction electrons to flip spins in certain directions and, therefore, to impose a friction on magnetization dynamics.…”