Interlayer Hopping Kinetics of Vacancies in CrI₃ Layers Leading to Monolayer/Bilayer Heterostructures

Abstract

Compared with monolayer CrI 3 , bilayer and few-layer CrI 3 structures attract more attention because they are more desired in practical applications, especially in magnetic sensing and data storage due to magnetoresistance effect. Both theoretical and experimental results show that the interlayer magnetic coupling depends on the stacking order. [9][10][11] Utilizing the antiferromagnetic coupling between CrI 3 layers, multiple-spin-filter magnetic tunnel junctions based on CrI 3 few layers were fabricated. [12,13] The tunneling magnetoresistance was reported to be enhanced with increasing the number of layers and reached to 19 000% when four-layer CrI 3 was used at low temperatures. [12] The interlayer magnetic coupling can be tuned not only by magnetic field but also by electric fields. [14] At fixed magnetic fields near the metamagnetic transition, Huang et al. realized voltage-controlled switching between antiferromagnetic and ferromagnetic states in bilayer CrI 3 . In addition, the magnetic properties of both monolayer and bilayer CrI 3 can be controlled by electrostatic doping using CrI 3 -graphene vertical heterostructures. [15] In bilayer CrI 3 , an electron doping above ≈2.5 × 10 13 cm −2 would change the interlayer coupling from antiferromagnetic to ferromagnetic even without any external magnetic field. [15] Lithium atom adsorption can change CrI 3 monolayer and multilayer from semiconductor to half-metal and enhance the ferromagnetism. [16] Moreover, the nonreciprocal second-order nonlinear optical effect in bilayer CrI 3 was 2D magnets, especially their multilayer structures exhibit promising applications in magnetic sensing and data storage due to magnetoresistance effect. Defects have significant influence on the performance of devices and are widely investigated for typical 2D magnets. However, the defects in multilayer structures are rarely studied. Here, based on density functional theory, an interesting synergy of the interlayer migration of I and Cr vacancies in bilayer CrI 3 is found. Cr vacancies attract I vacancies in adjacent layers and greatly reduce the intermigration barrier of I. On the other hand, I vacancies also facilitate the interlayer migration of Cr vacancies. A monolayer/bilayer heterostructure is expected to form after annealing at about 500 K due to the fast hopping of vacancies between layers and the strong driving force for vacancies clustering. The interlayer hopping and merge of vacancies help eliminate defect states in bilayer CrI 3 . These results provide an atomic-scale understanding of vacancy migration between CrI 3 layers, which is important for defect engineering and applications of bilayer and multilayer CrI 3 .

Magnetocrystalline Anisotropy and Magnetocaloric Effect Studies on the Room-temperature 2D Ferromagnetic Cr$_4$Te$_5$

“…It is known that in Cr x Te y systems the Curie temperature depends on various parameters such as sample thickness, sample composition, and on the method of preparation [71,72]. The critical exponents of β =0.485(3) and γ=1.202 (5) are close to the meanfield-like and 3D Heisenberg-like interactions, respectively, while the critical exponents of β =0.388 and γ=1.29 as reported in Ref. [25] in the bulk phase are found to be close to the 3D Heisenberg-like and meanfield-like interactions, respectively.…”

“…Investigation of the low dimensional magnetic materials with ferromagnetic ordering at room temperature has gained a lot of research interests in recent days due to their potential applications in the magnetic refrigeration and spintronic devices [1][2][3][4] for which the materials with strong magentocrystalline anisotropy are crucial [5,6]. In this regard, the van der Waals (vdW) magnets are of great interest from the fundamental science and advanced technological point of view due to their peculiar 2-dimensional (2D) magnetic properties [7][8][9][10] and strong magnetocrystalline anisotropy [11].…”

Experimental and computational Insights Into the magnetic anisotropy and magnetic behaviour of layered room-temperature ferromagnet Cr1.38Te2

“…Recently, several 2D magnetic materials such as CrI 3 (T C ≈ 45 K) [8], Cr 2 Ge 2 Te 6 (T C ≈ 61 K) [9], and Cr 2 Si 2 Te 6 (T C ≈ 32 K) [10] were synthesized with weak inter-layer coupling leading to strong magnetic anisotropy, but the T C of these systems is far below the room temperature (RT). Therefore, investigating the layered room-temperature 2D ferromagnetic materials with large magnetocrystalline anisotropy is crucial for potential applications in spintronics and data storage devices [11][12][13].…”

In-plane CrI2/CrI3 2D superlattices: novel electronic properties and strain induced phase transition

“…36 Various types of point defects in CrI 3 monolayers and bilayers have been investigated. [37][38][39][40] I vacancies can induce an out-of-plane switchable electric polarization in monolayer CrI 3 due to the symmetry breaking. 41 Heterostructure construction is an important method to control the properties of 2D materials and design related devices.…”

“…36 Various types of point defects in CrI 3 monolayers and bilayers have been investigated. 37–40 I vacancies can induce an out-of-plane switchable electric polarization in monolayer CrI 3 due to the symmetry breaking. 41…”