Peeling off Nanometer‐Thick Ferromagnetic Layers and Their van der Waals Heterostructures

Abstract

Since the discovery of graphene in 2004, [1] the family of van der Waals (vdWs) materials has been growing rapidly, presenting a wide range of novel physical properties, such as semiconductors with spin-valley coupling, [2] Ising superconductors, [3] topological semimetals with edge transport [4] and Mott insulators with tunable charge-density waves, [5] etc. The recent addition of magnetic crystals in the twodimensional (2D) material family, such as CrI 3 , Cr 2 Ge 2 Te 6 , and Fe 3 GeTe 2 , provides an ideal platform for fundamental understanding of 2D magnetism, as well as the applications of low-power spintronic devices. [6][7][8] The electrical control of 2D magnetic properties recently becomes possible, for example, conversion of bilayer CrI 3 from interlayer antiferromagnetism to ferromagnetism by electrostatic doping, [9,10] and electrical modulation of few-layer Cr 2 Ge 2 Te 6 coercivity and saturation field. [11] The advances of vdWs heterostructures can couple the quasiparticle interaction between the 2D magnetic material and others with engineered strain, chemistry, optical and electrical properties, providing an additional route to realize conceptual quantum phenomena and novel device functionalities, such as unprecedented control of the spin andThe recent discovery of 2D van der Waals (vdWs) magnetic crystals provides an ideal platform for fundamental understanding of 2D magnetism, as well as the applications of low-power spintronic devices. One can integrate 2D magnetic materials into vdWs heterostructures with engineered properties, and also manipulate the magnetism via electrostatic gating. However, due to their instability, the handing of 2D magnetic materials can only be carried out under the help of encapsulation with other 2D materials (such as hexagonal boron nitride (hBN)) in a glove box, which is the biggest barrier toward its practical applications. Here, an approach about peeling-off and transfer of 2D ferromagnetic (Ga,Mn)As layers with thickness of ≈10-20 nm grown by the molecular beam epitaxy under ambient conditions is introduced. Transmission electron microscopy characterizations confirm the singlecrystalline nature of the lifted-off (Ga,Mn)As. Superconducting quantum interference device measurements demonstrate that the lifted-off (Ga,Mn) As maintains its ferromagnetism. Using vdWs heterostructure assembly, technique hBN/(Ga,Mn)As top-gate Hall device and p-(Ga,Mn)As/n-MoS 2 heterojunction diode are fabricated. The electrical transport measurements demonstrate the ferromagnetic nature and gate tunable magnetoresistance of the lifted-off (Ga,Mn)As layer. This approach makes it possible to significantly expand the range of 2D ferromagnetic materials and their vdWs heterostructures.

Recent Advances in Two-Dimensional Magnets: Physics and Devices towards Spintronic Applications

“…Magnetoresistance (MR), referring to the resistance change in the presence of a magnetic field, is a significant physical quantity to reveal the spin-order effect on the electron scattering. Figure 3(d) shows the temperaturedependent magnetoresistance behavior of 2D ferromagnets (Ga,Mn)As, which are grown by low-temperature molecular beam epitaxy (MBE) [37]. At low temperature, two distinct peaks due to the anisotropic MR is observed, where MR is positive at low fields and negative at high fields.…”

“…copyright 2019 Physical Review X. Panel (d) is reproduced with permission from ref [37],. copyright 2019 Advanced Electronic Materials.…”

Van der Waals Heterostructures for Photoelectric, Memory, and Neural Network Applications

“…[ 65 ] Yuan et al also succeeded in exfoliating 10–20 nm 2D (Ga, Mn) of hundreds of micrometers from MBE‐grown substrates using the vdW heterostructure assembly technique. [ 66 ] They developed a deterministic dry transfer method and fabricated h‐BN/(Ga, Mn) as top‐gate Hall devices and p ‐(Ga, Mn)As/n‐MoS 2 heterostructure diodes. The results helped to extend the 2D ferromagnetic material system and the related vdW heterostructures.…”

“…Images adapted and reprinted with permission. [63][64][65][66][244][245][246] Copyright, 2016 and 2017, American Chemical Society. Copyright 2018 and 2020, American Association for the Advancement of Science; Copyright 2014, 2016, and 2017, Springer Nature.…”

Nanomaterials Based Micro/Nanoelectromechanical System (MEMS and NEMS) Devices

“…Using this technique, the isolation of layers can be controlled down to a monolayer, and the flake size depends on how available are the large crystals for exfoliation. This technique can be applied to any bulk-layered crystals whose layers are held together by interlayer weak van der Waals interactions [22,23].…”