Investigation Of Magnetism In Single-Atom Transition Metal Anchored Graphite Materials

With the continuous development of human society,the blowout growth of information and the arrival of the post-Moore's Law era have put forward new requirements for the storage and security of information,which is an important issue to be solved urgently.The data storage of traditional semiconductor devices has disadvantages such as small capacity,low density,high energy consumption and easy loss of information,which can hardly meet the needs of information development in the new era.The rapid development of spintronics in the past few decades has realized the dual control of electron charge and spin.Spintronics devices have brought a new way to solve the above problems.Spintronic devices can control their electromagnetic performance in different dimensions,with their storage density and security are improved,size and power consumption are greatly reduced,and thus have become the latest generation of electronic devices attracting wide attention and research.Two-dimensional(2D)materials have become a research hotspot in the field of condensed matter physics because of their excellent physical and chemical properties.Among them,monolayer graphene was prepared in 2004,and its electromagnetic properties have been extensively studied and regulated.However,2D graphite materials do not have intrinsic magnetism,and thus hinders their application in spintronic devices.Therefore,how to successfully introduce intrinsic ferromagnetism into 2D graphite materials and control related properties is the key problem to break this bottleneck.In this paper,2D graphite nanosheets were prepared by high temperature synthesis in a tubular furnace,and several transition metal elements were anchored on these nanosheets in the form of single-atom groups,thus successfully inducing room-temperature ferromagnetism in 2D graphite materials.Meanwhile,the relationship between ferromagnetism and the amount of transition metal elements introduced was also studied.Finally,the physical origin of the obtained magnetism is explored by means of density functional theory calculation.Our work provides experimental and theoretical bases for the application of 2D graphite materials in spintronics.The main contents are as follows:1.Pure 2D graphite nanosheets and Cr-N₃group anchored graphite nanosheets were prepared by high temperature synthesis.By adjusting the content of Cr(NO₃)₃precursor,three kinds graphite nanosheets with different Cr-N₃group anchored concentrations were obtained.The magnetic measurements show that these Cr-N₃group anchored graphite nanosheets have intrinsic ferromagnetism at room temperature,and the ferromagnetism is directly related to the amount of introduced Cr-N₃groups.And the maximum M_sis 0.051 emu/g.The first-principles calculation further shows that the introduction of Cr-N₃groups successfully induces net spin moments in graphite nanosheets,which leads to spontaneous magnetization,and thus forms the long-range magnetic ordering within a certain range.2.On the basis of the above preparation method,Mn(NO₃)₂·4H₂O was used as the precursor to prepare two graphite nanosheets with different Mn-N₄group concentrations.Magnetic measurements show that the two samples exhibit obvious intrinsic ferromagnetism,and the ferromagnetism is directly related to the amount of Mn-N₄groups introduced.Its maximum M_sis 0.072 emu/g.The first-principles calculations indicate that the Mn-N₄group is the source of ferromagnetism.In order to further explore the maximum doping concentration anchored in the form of Mn-N₄single-atom group,we continued to increase the dosage of the precursor,and finally found three N-doped MnO samples with different concentrations,all of which showed intrinsic ferromagnetism.And the mechanism is explained by first principles calculation and ferromagnetic double exchange interaction.