Investigation Of Ferromagnetism In Two-dimensional Carbon-based Ultrathin Materials

In recent years,the rapid development of the semiconductor technology has promoted the continuous progress of society and technology.However,due to the explosive growth of the information,the disadvantages of traditional semiconductor equipment are becoming increasingly prominent.In order to solve these problems,spintronics devices that can control both the charge and spin degrees of electron have become an emerging field.At the same time,two-dimensional?2D?metal-free materials have the advantages of low power consumption and weak spin-orbit interaction due to their singular characteristics.They are regarded as ideal materials for preparing spintronics devices.However,experimentally achieving high-temperature ferromagnetism in 2D metal-free materials is still a challenge.In this work,2D metal-free g-C₃N₄ and graphene are prepared and realized their high temperature ferromagnetism.Combined with theoretical calculations,we conducted in-depth discussions on the magnetic properties of the samples.The main contents are as follows:1.2D non-metal g-C₃N₄ nanosheets doped with light elements,such as F,B and P,were prepared by thermal polymerization.The magnetic test results prove that F,B and P doping can effectively introduce high-temperature ferromagnetism into 2D non-metal g-C₃N₄ nanosheets with Curie temperatures of F:700 K,B:951 K,and P911 K,respectively.In addition,we have studied the origin of the ferromagnetism in detail in conjunction with first-principle calculations.It is worth noting that we have discovered the semi-metallic properties in F and B doped g-C₃N₄ nanosheets.2.g-C₃N₄ nanosheets with interlayer structure distortion and N vacancy were prepared by atmosphere annealing or metal co-annealing method.The magnetic measurement results prove that the structurally distorted g-C₃N₄ nanosheets and g-C₃N₄ nanosheets with N vacancy are ferromagnetic,and the Curie temperature of the N-vacancy g-C₃N₄ nanosheet is as high as 926 K.By adjusting the annealing time,we find that the magnetic properties of the structurally distorted g-C₃N₄ and N-vacancy g-C₃N₄ nanosheets depend on the annealing time,and their maximum saturation magnetizations are 0.003 emu/g and 0.005 emu/g,respectively.3.The metal co-annealing method can realize the denitrification of g-C₃N₄.By adjusting the annealing temperature and annealing time,we have achieved the transition from g-C₃N₄ to N-doped graphene and observed the high-temperature ferromagnetism in N doped graphene.The pretty high Tc?1034 K for N doped graphene?of ferromagnetic signals are observed,and the saturation magnetization of N doped graphene could be precisely controlled.Combining with theoretical simulation results,we attribute the intrinsic ferromagnetism to nitrogen dopant in the samples.