| Spintronics devices combine the basic characters of spin and charge, which is one of the hot researches in the materials science and condensed matter physics. The material with high spin polarization plays a key role in enhancing the efficiency of spintronics devices. The conductance spin polarization and Curie temperature of bulk Fe4 N are-100% and 767 K, respectively. Therefore, Fe4 N is considered as a promising spintronic material for practical application in magnetic tunnel junctions and spin injection.In this dissertation, the electronic structure and magnetism of Fe4N/Oxides?Mg O, Ba Ti O3, Bi Fe O3? interface and the magnetoelectric coupling effect of La2/3Sr1/3Mn O3/T-Bi Fe O3 supperlattices are studied by density functional theory to provide the theoretical basis for magnetic tunnel junctions, the spin injection of Fe4N/Si?Graphene, MoS2? heterostructures and the electronic and magnetic properties of Fe-X6?X=S, C, N, O, F? doped monolayer MoS2 are calculated to provide the theoretical basis for spin injection.By calculating the cohesive energy, band structure, density of states, Schottky barrier, charge density difference and plane-averaged charge density difference, it is found that the n- and p-type doping of Mg O are induced in the Fe?Fe?/Mg O and(Fe?)2N/Mg O interfaces, respectively. The metallic characteristics are induced in Ba Ti O3 by contact with Fe?Fe? termination, followed by p-type doping in the(Fe?)2N/Ba O interface and n-type doping in the(Fe?)2N/Ti O2 interfaces, respectively. The deposition of Fe4 N on Bi Fe O3 can result in a metallic Bi Fe O3. The different electronic and magnetic properties are governed by different interfacial bonding.By calculating the work of separation, band structure, density of states and charge density difference of La2/3Sr1/3Mn O3/T-Bi Fe O3 superlattices, it is found that the energetically favorable interface consists of La O-terminated La2/3Sr1/3Mn O3 and Fe?OB?2-terminated Bi Fe O3. The superlattice exhibits a half-metallic character, as is desired for spintronics devices. As compared to La2/3Sr1/3Mn O3/R-Bi Fe O3 superlattice, the La2/3Sr1/3Mn O3/T-Bi Fe O3 superlattice is characterized by a strongly enhanced electric control of the magnetism. At the Fe?OB?2-Sr O, Fe?OB?2-Mn O2, Bi OA-Sr O and Bi OA-La O interfaces, the ferromagnetic ordering of Fe and Bi implies the presence of exchange bias effect.By calculating the cohesive energy, band structure, density of states, charge density difference and plane-averaged charge density difference of Fe4N/?Si, Graphene? bilayers, it is found that strong Fe4N-Si interfacial bonding induces the spin polarization of Si, whereas, the weak interaction between Fe?Fe?, N and Graphene shifts the Fermi level of Graphene downward with respective to Dirac point. A larger Fermi level-shift of latter can be attributed to a larger difference of work functions between N-terminated surface and Graphene.By calculating the work of separation, band structure, density of states, Schottky barrier and charge density difference of Fe4N???/MoS2? ??? ×???? superlattice, it is found that strong Fe?Fe?-S interfacial hybridization results in magnetism of monolayer MoS2, with a magnetic moment of 0.33 ?? for Mo located on top of Fe?. The weak N-S interfacial bonding leads to the appearance of p-type Schottky barrier and the increasing of the band gap of monolayer MoS2.By calculating the band structure, density of states and charge density difference of Fe-X6 clusters?X=S, C, N, O, F? doped monolayer MoS2, it is found that single Fe and Fe-F6 substitutions make the system display half-metallic properties, Fe-C6 and Fe-F6 substitutions lead to a spin gapless semiconducting behavior, and Fe-O6 doped monolayer MoS2 is semiconducting. The different electronic and magnetic characters originate from hybridization between the X and Fe/Mo atoms. |
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