Preparation And Characterization Of Van Der Waals Force Two-dimensional Magnetic Material CrCl₃

The emergence of two-dimensional materials broke the traditional concept that two-dimensional crystals with atomic layer thickness cannot exist independently and stably due to thermodynamic instability.Their excellent properties have attracted widespread attention.In recent years,the continuous development of two-dimensional intrinsic magnetic materials has provided new opportunities and development directions for the development of information storage,information coding,spintronics device.As the requirements for device integration become higher and higher,the atomic-thick magnetic multilayer film is bound to be important material for the next generation of spintronics devices.The two-dimensional magnetic van der Waals crystal has novel electrical and magnetic properties,and it has great potential in the development of low-dimensional and high-density spintronic devices.When the atomically thin material is exfoliated from the layered bulk magnetic crystal and maintains its magnetic order,the two-dimensional magnetic layer can be produced,which promotes the study of low-dimensional magnetism and the development of new spintronics heterostructures,which brings opportunities and challenges for the research of more new physical phenomena.In the family of two-dimensional magnetic layers,chromium trihalide CrX3(X=Cl,Br,I)is one of the first materials to be found to exhibit single-layer magnetism,and is a good candidate material for spintronics device.Bulk CrCl3 is a layered insulator.The weak van der Waals force between the layers and the in-plane ferromagnetism make it very promising as a singer-layer magnet and a material for manufacturing van der Waals heterostructures.This paper focuses on the two-dimensional interlayer antiferromagnetic insulator CrCl3,and studies its grow conditions and exfoliation methods,surface morphology and structural phase transition properties,low temperature magnetic properties and high frequency antiferromagnetic resonance properties.In this article,we have successfully prepared CrCl3 bulk crystals using physical vapor deposition.Because of its weak interlayer van der Waals force,we used mechanical exfoliation method to exfoliated it to the single layer.We measured the thickness of ultra-thin samples using optical microscopy and atomic force.The structure of CrCl3 was characterized by X-ray diffraction and Raman spectroscopy,and its energy band structure was characterized by measuring its photoluminescence spectrum.It was found that as the temperature increased,the peak value shifted to low frequency,indicating that CrCl3 changes from the low-temperature rhombohedral phase to the high-temperature monoclinic phase,and the phase transition temperature is about 240 K.Using the superconducting quantum interferometer to measure magnetism,it is found that CrCl3 is in-plane anisotropy with a Neel temperature of 14 K.When the temperature is lower than 14 K,its antiferromagnetic Neel vector is in the plane.The inter-antiferromagnetic exchange coupling field is about 105 mT,and the spin flipping field is about 11 mT.CrCl3 layers are coupled ferromagnetically at 14-21 K,and when it is above 21 K,CrCl3 is paramagnetic.In the antiferromagnetic resonance measurement,CrCl3 exhibits two resonance modes in the GHz band,and it has a completely different ?-H dispersion relationship.The rich dynamic response indicates that CrCl3 is a material with a low antiferromagnetie resonance frequency,and has a wide range of applications.In summary,we verified that CrCl3 has the following characteristics.we can prepare the bulk CrCl3 easily.It is stable in the air,and can control the magnetic order under a relatively small external magnetic field at low temperatures,and CrCl3 monolayer is a kind of two-dimensional materials with intrinsic ferromagnetism and semiconductor characteristics,which facilitate the integration of magnetism into van der Waals heterojunctions for wider applications.