First-principles Study On Magnetism And Magnetocrystalline Anisotropy Of Low-dimensional Semiconductors

Low-dimensional semiconductors with high magnetocrystalline anisotropy are essential for next-generation spintronic devices.However,most of the fabricated low-dimensional semiconductors are intrinsically nonmagnetic,the fabricated low-dimensional ferromagnetic semiconductors are fewer and their Curie temperatures are very low.Therefore,for realizing the applications of low-dimensional semiconductors in spintronic devices,it is necessary for develop approaches to induce magnetism and high magnetocrystalline anisotropy in nonmagnetic low-dimensional semiconductors and exploring new low-dimensional ferromagnetic semiconductors with large magnetocrystalline anisotropy and high Curie temperatures.Above all,the thesis are studied based on first principles calculations and the main results are as follows:1.Selecting the low-dimensional semiconductor that can be compatible with the fabrication process for modern silicon-based semiconductors——silicene to build Fe/silicene heterostructures,we investigate the magnetism and the magnetocrystalline anisotropy of the Fe/silicene systems and the influence of an external electric field on the magnetism and the magnetocrystalline anisotropy of the Fe/silicene heterostructures.The results show that the magnetic moments and the magnetocrystalline anisotropy of the Fe/silicene heterostructures are mainly from Fe films.With increasing the thickness of Fe film,the Fe/silicene heterostructure changes from perpendicular magnetocrystalline anisotropy to in-plane magnetocrystalline anisotropy.In addition,the magnetic moments in all the Fe/silicene heterostructures are insensitive to the electric field.Under the positive electric field,for the different Fe/silicene systems,the perpendicular magnetocrystalline anisotropy is enhanced and the in-plane magnetocrystalline anisotropy is weaken.The mechanism of the electric-field-driven modulation of magnetocrystalline anisotropy is mainly from the increase of the positive contribution from spin-orbit coupling interaction between opposite spind_{y z}andd_z2 orbitals of the fourth Fe layer from the Fe/silicene interface.2.We systematically investigate the electronic structure,stability,Curie temperatures and magnetocrystalline anisotropy of the unstrained and strained Ni I2 monolayers.The results show that the Ni I2 monolayer is a ferromagnetic semiconductor with an indirect band gap of 2.33 e V.The magnetic moment of 2.0?_Bper Ni I₂ unit cell is mainly come from Ni atom.Our calculated results also show that unstrained Ni I2 monolayer is with in-plane magnetocrystalline anisotropy energy of-0.11 me V/unit cell and Curie temperature of 79 K.Moreover,we predict that the Ni I2 monolayer under the-4%?4%strains are dynamically and thermally stable.It is worth noting that the in-plane magnetocrystalline anisotropy and the Curie temperature of the Ni I2 monolayer can be simultaneously enhanced under the compressive strain.In particular,the in-plane magnetocrystalline anisotropy of the Ni I2 monolayer under the-4%compressive strain is more than three times compared with that of unstrained system.The reason for the enhancement of in-plane magnetocrystalline anisotropy by compressive strain is that the increase of the negative contribution from spin-orbit coupling interaction interaction between opposite spinp_x andp_y orbitals of I atom.