Screening Magnetic Two-Dimensional Atomic Crystals with Nontrivial Electronic Topology

Abstract

To date only a few two-dimensional (2D) magnetic crystals were experimentally confirmed, such as CrI 3 and CrGeTe 3 , all with very low Curie temperatures (T C ). High-throughput first-principles screening over a large set of materials yields 89 magnetic monolayers including 56 ferromagnetic (FM) and 33 antiferromagnetic compounds.Among them, 24 FM monolayers are promising candidates possessing T C higher than that of CrI 3 . High T C monolayers with fascinating electronic phases are identified: (i) quantum anomalous and valley Hall effects coexist in a single material RuCl 3 or VCl 3 , leading to a valley-polarized quantum anomalous Hall state; (ii) TiBr 3 , Co 2 NiO 6 and V 2 H 3 O 5 are revealed to be half-metals. More importantly, a new type of fermion dubbed type-II Weyl ring is discovered in ScCl. Our work provides a database of 2D magnetic materials, which could guide experimental realization of high-temperature magnetic monolayers with exotic electronic states for future spintronics and quantum computing applications. KEYWORDS: Magnetic two-dimensional crystals, high throughput calculations, quantum anomalous Hall effect, valley Hall effect. 2 / 12The discovery of two-dimensional (2D) materials opens a new avenue with rich physics promising for applications in a variety of subjects including optoelectronics, valleytronics, and spintronics, many of which benefit from the emergence of Dirac/Weyl fermions. One example is transition-metal dichalcogenide (TMDC) monolayers, whose finite direct bandgap enable novel optoelectronic controls as well as valley-dependent phenomena, such as circular dichroism and valley Hall effect (VHE) 1-2 . Due to the equivalent occupation of K and K' valleys in TMDC materials, the VHE does not produce observable macroscopic Hall voltage. This is overcome in magnetic counterparts, resulted from time reversal symmetry breaking 3-8 .In contrast to fermions in nonmagnetic systems, such as massless Dirac fermions in borophene, black phosphorus, Cu 2 Si 9-13 , and massive Dirac fermions in graphene and bilayer bismuth 14-15 , few types of fermions in 2D magnetic systems are proposed, implying the scarcity of intrinsic magnetic 2D crystals. In particular, 2D magnets with massive Dirac fermions can support quantum anomalous Hall state leading to topologically protected spin current, promising for low-power-consumption devices. Unfortunately, the state is only realized in 2D materials with non-intrinsic magnetism at extremely low temperature (e.g. 30 mK for Cr-doped (Bi,Sb) 2 Te 3 thin film) [16][17][18][19][20][21][22] , hampering its extensive applications. Therefore, discovery of 2D magnets at an elevated temperature is of great importance, providing optimal platforms to enable realistic spintronic and quantum devices, as well as to realize new electronic states.To date 2D magnetic materials are limited to marginal modifications to existing compounds, for instance by: (i) adsorbing hydrogen on graphene 23 ; (ii) reconstructing surface/edge [24][25] ; or (iii) creating defects in MoS 2 n...

Strain-Induced Room-Temperature Ferromagnetic Semiconductors with Large Anomalous Hall Conductivity in Two-Dimensional Cr2Ge2Se6

“…It is noted that for simplicity the Ising model is applied in our Monte Carlo simulation, while the Heisenberg model with magnetic anisotropy was suggested in experiment [6]. In addition, the estimated Curie temperature T c could be even larger by using the mean field approximation [17]. The calculated Curie temperature for monolayer Cr 2 Ge 2 Se 6 is T c = 144 K, which is about 5 times higher than the T c = 30 K for monolayer Cr 2 Ge 2 Te 6 by the Monte Carlo simulation.…”

“…Despite the relatively small number of monolayer ferromagnetic materials realized in experiment, predicting promising candidates by first principles calculations can provide reliable reference for experiments [14,15]. Researchers have also studied possible * gubo@ucas.ac.cn † gsu@ucas.ac.cn 2D ferromagnetic materials by machine learning [16] and high-throughput calculations [17].…”

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

“…There is still a strong contemporary debate around the origin of 2D magnetism in VSe 2, particularly surrounding the role of the substrate‐film interactions, and it is of great interest to see if it can be widely reproduced and utilized by other groups. Recently, a substantial number of additional 2D ferromagnets has been predicted by theory, see Shabbir et al Systematic theoretical screening for vdW crystals with possibly the highest Curie temperatures has recently been published to identify new candidates for ML magnetism. The highest transition temperatures exceeding 1000 K have been predicted in so‐called “Mxeneˮ compounds, having the formula M 2 AX 2 where M is a metal (Mn, Cr, Ti), A = (C, N), and X = (O, OH, F, Cl).…”

Prospects and Opportunities of 2D van der Waals Magnetic Systems

“…Recently, some studies designed algorithm to computationally screen 2D magnetic materials from materials database. [ 115‐118 ] These algorithms focus on finding materials with layered structure and low exfoliation energy. [ 116‐119 ] The electronic and magnetic properties are then calculated by first principle.…”