Novel Two-Dimensional Magnetic Materials: Theoretical Design And Performance Regulation

Traditional electronic devices work by controlling charge.In order further expand the functionality and performance of electronic devices,researchers use electronic spin as information carrier.Electronic devices that use spin as an information carrier are called spintronic devices.Compared with traditional electronic devices,spintronic devices have the advantages of non-volatility,low power consumption,fast response speed and high integration.As the carrier of spintronic devices,magnetic materials have always played an important role in the field of spintronics.In recent years,two dimensional ferromagnetic materials have been successfully prepared,introducing spintronics into the two dimensional world.Two-dimensional materials have low-dimensional characteristics completely different from three-dimensional materials,showing large specific surface area,easy stacking characteristics and excellent magnetic,electrical and optical properties,which have attracted extensive attention from researchers.Thermal fluctuations make it difficult for two-dimensional materials to maintain long-range magnetic order in finite temperature.It is of great significance to introduce magnetism into two-dimensional materials and find intrinsic ferromagnetic two-dimensional materials for the development of two dimensional spintronics.With the development of research,the application of two-dimensional magnetic materials to spintronic devices has become a new hot and difficult point in the field.This article employs density functional theory and non-equilibrium Green’s function method to investigate magnetic engineering in new two-dimensional non-magnetic materials,predict the performance of new two-dimensional ferromagnetic half metals,and control the performance of two-dimensional ferromagnetic semiconductors.The study successfully achieved magnetic induction in two-dimensional silicon isotropic bodies and predicted the existence of two stable ferromagnetic spin-half metal materials.Additionally,the study successfully induced the half-metallicity and controlled its magnetic anisotropy in the two-dimensional intrinsic ferromagnetic semiconductor CrI₃.Moreover,a new two-dimensional magnetic tunnel junction model is proposed to solve the problem of complex interfaces,which prevents the loss of electrode half-metallicity in traditional three-dimensional half metal electrode tunnel junctions.This model has the potential to achieve extremely high tunneling magnetoresistance in experiments,providing new ideas for the potential applications of two-dimensional materials in spintronics.The main research contents are as follows:（1）Based on the structural design of silicon materials,fifteen direct band gap silicon allotropes with zeolite characteristics are first predicted.Through further screening of the zeolite framework silicon allotropes,two stable two-dimensional zeolite framework silicon allotrope are proposed.Based on the large holes and cages in the zeolite framework,which are easy to adsorb atoms and molecules,the adsorption characteristics of transition metal elements by the new two dimensional zeolite framework silicon allotrope were studied,and the net magnetic moment was successfully induced in the two dimensional non-magnetic silicon material,so that it can meet the electrical and magnetic characteristics of the application of spintronic devices.（2）The stability,electrical properties and magnetic properties of two dimensional transition metal ternary compounds,Mn GeSe₃ and Mn GeTe₃,have been studied.It is found that they are both half metal with intrinsic ferromagnetism.The ferromagnetic phase transition of monolayer MnGeX₃（X=Se,Te）material was analyzed by Monte Carlo simulation method based on Ising model.The influence of interlayer interaction on the electrical and magnetic properties of CrI₃/MnGeX₃ heterojunction and its mechanism are studied.In terms of electrical properties,the interlayer charge transfer successfully induces the half metallic property in CrI₃,but the electronic structure near the Fermi surface is completely different in the two heterostructures.In terms of magnetic properties,the easy magnetization axis of CrI₃ in the CrI₃/Mn GeSe₃ is flipped from out-of-plane to in-plane,while the magnetic properties of CrI₃ in the CrI₃/Mn GeTe₃ are not affected by the interlayer interaction.Further study shows that the two heterostructures have completely different charge transfer directions,which leads to the different electronic and magnetic properties of CrI₃ layers,and also leads to different regulatory effects of normal strain on the two heterojunctions.This work provides a theoretical basis for the theoretical prediction and performance regulation of two dimensional ferromagnetic materials.（3）We design a lateral magnetic tunnel junction model with structure of（CrI₃/MnGeX₃）/CrI₃/（CrI₃/MnGeX₃）by using the CrI₃/MnGeX₃（X=Se,Te）heterostructure.The proposed model for magnetic tunnel junctions avoids the loss of spin-half-metallicity caused by complex interfaces,making it highly promising for achieving extremely high tunneling magnetoresistance in experiments.First-principles studies demonstrate that the new magnetic tunnel junction exhibits remarkably high tunneling magnetoresistance.The highest values of tunneling magnetoresistance,amounting to 614848%and 14729340%,respectively,are observed in CrI₃/Mn GeSe₃-based and CrI₃/Mn GeTe₃-based lateral magnetic tunnel junctions,which is consistent with the expected performance of spin-half-metallic electrode magnetic tunnel junctions.The study investigates the tunneling mechanism under bias voltage and the impact of different spin injection methods on tunneling magnetoresistance.Additionally,the relationship between the bandgap of electrode spin-half-metallic materials and the decay threshold voltage of tunneling magnetoresistance in magnetic tunnel junctions is uncovered.Notably,the larger the bandgap of the electrode spin-half-metallic material,the greater the decay threshold voltage of TMR in magnetic tunnel junctions.Finally,the study examines the role of normal strain in the modulation of spin transport properties of magnetic tunnel junctions and finds that normal strain effectively enhances the tunneling magnetoresistance and the threshold voltage of magnetic resistance decay in devices.This work provides fresh insights and theoretical validation for the prospective utilization of spin-half-metallic materials in spin electronic devices.