Research On Magnetic And Electric Properties Of New Strongly Correlated Spintronic Materials

Spintronics is the second-generation electronics, it has great potential application in information, materials, military or other fields. Compared with ordinary magnetic materials, half-metallic ferromagnets(HMFs) have higher spin polarization at the Fermi level(Ef), and then higher magnetoresistance effect. Therefore they have important position in spintronic devices design and application.In this paper, some new HMFs with high Curie temperature, stable structure, the stable half-metallicity and other rich physical properties are explored by the first principles calculation based on density functional theory. Tm-doped ThO, Eu-doped ThO and pure compound SmX are optimized geometrically. Then their magnetic and electric properties including the formation energy, density of states, band structure, charge distribution et al are calculated in detail. Then their microscopic mechanism of magnetic and electric properties are analyzed based on the ligand field theories. The main works and results are as follows:(1) The geometric structures of the doped salt-rock compounds Th0.75Tm0.25 O are optimized, where Th=Be, Mg, Ca, Sr, Ba and Tm=Ti, V, Cr, Mn. Then their spin-polarization state densities are calculated. Their electronic structures and the microscopic mechanism of magnetic and electric properties are analyzed deeply based on the crystal theory. Results show that Mg0.75V0.25 O, Mg0.75Cr0.25 O, Mg0.75Mn0.25 O, Ca0.75V0.25 O, Ca0.75Cr0.25 O, Ca0.75Mn0.25 O, Sr0.75V0.25 O, Sr0.75Cr0.25 O and Sr0.75Mn0.25 O have spin-up free carrier near the Ef so these materials have up-spin sub-band. This shows that their conductivity of the system are improved obviously. On the other hand, they all have integral mangetic moments. For examples, the supercell magnetic moments of V-doped materials, Cr-doped materials and Mn-doped materials are 3.00, 4.00 and 5.00 ?B, respectively. Their magnetism, conductivity and half-metallicity come mainly from the spin-polarization of Tm(Tm=V, Cr, Mn) 3d-orbitals.(2) The geometric structures of the rare earth-doped compounds Th0.75Eu0.25 O are optimized, where Th=Be, Mg, Ca, Sr, Ba. Then their spin-polarized state densities and other band structures are calculated. Their electronic structures and the microscopic mechanism of magnetic and electric properties are analyzed in detail based on the crystal theory. Results show that their spin-polarization is all +100% at Ef and their supercell magnetic moments are all 7.00 ?B, so they are typical HMFs. The calculations of formation energy show that Sr0.75Eu0.25 O and Ba0.75Eu0.25 O is easily prepared experimentally, but it is difficult to Ca0.75Eu0.25 O experimentally. Their energy gaps and half-metallic gaps are wide so that they all have high Curie temperatures and stable half-metallicity. Therefore, they have great application potential in spintronics. The magnetic moments, the conductivity and the half-metallicity come mainly from the spin-polarization of Eu 4f-orbitals.(3) The geometric structures of the salt-rock structure SmX(X=O, S, Se, Te) are optimized. Then their band structure, state densities and charge distribution are calculated in system. Results show that these materials only have up-spin sub-bands at Ef and their net supercell magnetic moments are all 24.00 ?B, so they are evidently HMFs. The magnetic moments, the conductivity and the half-metallicity of SmX come mainly from the spin-polarization of Sm 4f-orbitals, which are caused by strong octahedral crystal field in the ligand compound ML6 consisting of the Eu-ion and six O-ions around it.