The Research Of Magnetic Phase Transition Of Van Der Waals Magnetic Materials CrOCl

Since graphene opened the door to the two-dimensional world,which have be-come a hot research subject for their adjustable bands and abundant heterojunction.Magnetism in two-dimensional materials,due to its strong internal spin fluctuations,is highly expected in fundamental research and industrial applications.The introduction of this thesis presents the magnetism in solids and 2D magnetic materials.Section 1.1 starts with the magnetic ordered classification of solids,focus-ing on the intrinsic mechanism and macroscopic manifestations of ferromagnetism and anti-ferromagnetism.Section 1.2 elaborates the unique properties and wide application of 2D materials.2D magnetic materials were introduced then.Due to dimensional inhi-bition and spin-lattice coupling,2D magnetic materials offer broad prospects for both theoretical and practical application development.After that,the optical and electrical study of two van der Waals magnetic materials CrI3 and Cr2(Si,Ge)2Te6 in a few lay-ers or even a single layer is introduced.The optical study of Kerr effect of CrI3 and Cr2Ge2Te6 provides the most direct evidence for the existence of long-range magnetic ordering under the van der Waals magnetic material.The subsection 1.2.3 illustrates the fact that the above two materials still have a low TC for practical applications,and introduces the theoretical prediction of a single layer of high TC van der Waals mag-netic material CrOCl,which explaining the research motivation,with the review of the former research development on CrOCl.The last section of this chapter introduces the research motivation and research content of this paper.The second chapter introduces the research methods used in this paper.Section 2.1 first reviews the basic principles of crystal growth and outlines the most of the methods of crystal growth.Next,the two main methods of laboratory synthesis of crystals,co-solvent and chemical vapor transport methods are introduced.The his-tory and the principle of chemical vapor transport methods is introduced,reviewing the methods summarized by the predecessors.Section 2.2 introduces the properties mea-surement methods adopted in this paper,including magnetization measurement,specific heat measurement,magnetic susceptibility measurement under pulsed strong magnetic field and magnetic force microscopy.The principle and practical operation methods of the pulsed field and magnetic force microscopy used in this study are emphasized.The third chapter is the study of the variable magnetic phase transition of Van der Waals semiconductor material CrOCl bulk material.Firstly,we introduce the synthesis method of chemical vapor transport of single crystal samples,and the characterization method by X-ray diffraction and photoelectric spectroscopy.By magnetic susceptibility measurement,we found that the variable magnetic phase transition existing in the low field.In the section 3.4,for the first time,we observed the magnetic domain change during the phase transition by magnetic force microscopy,and found strong anisotropy on the surface of the sample.Further more,we measured the relation between the mag-netization and the magnetic field at the 35 T high field In the Wuhan Pulse Field Labo-ratory.Combining specific heat we improved the magnetic phase diagram in high field.Section3.5 reports on our preliminary work on low-dimensional bulk materials,and our success to obtain the single-layer samples.The last chapter is an overall summary and outlook for future work.Magnetism is the most complex and ubiquitous phenomenon in condensed matter physics.2D ma-terials are materials whose degree of freedom is highly suppressed.The superposition of the two makes the behavior of 2D magnetic materials variously.In this paper,we have made a further study on the behavior of bulk magnetization,which deepens peo-ple’s understanding of the internal mechanism of 2D magnetic materials,and lays the foundation for further research on magnetic behavior in low dimensions.In the future,van der Waals heterogeneous junctions can be fully utilized by taking advantage of the properties of Van der Waals’ flat interface,to provide broad prospects for diverse appli-cations.