Bo Wu

Geometrical structure and spin order of Gd13 cluster

The spin-polarized generalized gradient approximation to the density-functional theory has been used to determine the lowest energy structure, electronic structure, and magnetic property of Gd(13) cluster. Our results show that the ionic bonding is combined with the covalent characteristics in stabilizing the Gd cluster. The ferrimagnetic icosahedron is found to be the lowest energy configuration, in which the centered Gd atom couples antiferromagnetically with the rest Gd atoms surrounding it. No spin non-collinear evidence has been detected in our calculations. It is identified that the local magnetic moments of Gd atom are about 8 μ(B) regardless of geometrical structure. Finally, the comprehensive electronic structure analyses show that the indirect long-range magnetic coupling between the polarized 4f is mediated by the polarization of 5d, 6s, and 6p conduction electrons, which is the typical Ruderman-Kittel-Kasuya-Yosida interactions.

Tunable Magnetism and Half-Metallic Stability in Si-Doped Hg2CuTi-Type Ti2CoGa Alloy

Using the ab-initio calculations within the density functional theory (DFT), we have investigated the electronic structure, magnetism and half-metallic stability of Si-doped Heusler compound Ti2CoGa with Hg2CuTi-type structure. The results revel that the lattice constants and total magnetic moments in per unit obey the Vegard’s rule and the Slater-Pauling rule well, respectively. The most stable half-metallicity occurs at doping concentration x=0.75 because the Fermi level is located at the middle of the spin-minority gap. Our studies also indicate that the competition between RKKY-type indirect exchange and direct hybridization of d-electronic atoms plays a dominating role in determining the magnetism.

An Investigation of Half-Metallic Ferromagnets Behavior in Hg2CuTi-Type Heusler Alloy Ti2FeAl by Using GGA

By using generalized gradient approximation (GGA) scheme within the density functional theory (DFT), the electronic and magnetic properties of Hg2CuTi-type Heusler alloy Ti2FeAl were investigated. The results reveal that a 100% spin polarization appears at Fermi level (εF) in Ti2FeAl, and is maintained during lattice range of 5.1Å~6.2Å. Ti2FeAl is one of stable Half-Metallic Ferromagnets (HMF) with a spin-minority gap of 0.5 eV at εF and total magnetic moment of 1μB per unit cell. Our studies also indicate that the competition between RKKY-type indirect exchange and direct hybridization of d-electronic atoms plays a dominating role in determining the magnetism.

Effect of Nb Doping on Electronic and Magnetic Properties of Heusler Alloy Ti2NiAl with Hg2CuTi-Type Structure

In this work, the electronic and magnetic properties of Nb-doped full-Huesler alloy Ti2NiAl with Hg2CuTi-type structure have been investigated by using first-principles calculations within the density function theory (DFT). Due to the Nb which has less valence electrons than Ni doping into Ni-site, the gap around the Fermi level of the compound Ti2Ni1-xNbxAl (0≤x≤1) is gradually narrowed, and destroyed completely as x≥0.5. With the increase of x, it has gone through the transition from the ferromagnetism to the non-magnetism, and then to the ferromagnetism finally. Further analyses of density of states reveal that the d-electronic rehybridization induced by Nb-doping and RKKY-type indirect interaction is directly responsible for the changes of half-metallicity and magnetism.

Electronic Structure and Magnetic Properties of Ga-Doped Heusler Alloy Co2FeSi

Using GGA+U (UCo =2.1eV, UFe=2.5eV) scheme based on the density functional theory (DFT), we investigate the electronic structure, magnetism and half-metallic stability of Ga-doped Heusler compound Co2FeSi. We find that the lattice constants and total magnetic moments in per unit respectively obey the Vegard’s rule and the Slater-Pauling rule well. The most stable half-metallicity occurs at doping concentration x=0.5 due to the Fermi level is situated slightly above the middle of the spin-down gap. Our studies also indicate that the RKKY-type exchange mechanism plays a dominating role in determining the magnetism of HMFs.

Atom-Rich and Defect Effects on Electronic Structure and Magnetism in Co2MnGe/MgO Heterojunction

We investigated the atomic rich and defect effects on the half-metallicity of the full-Heusler alloy Co2MnGe from the first principles. Our results show that both Mn-rich and Co-rich could increase the tunnel magnetoresistance (TMR) of the Co2MnGe/MgO magnetic tunnel junctions (MTJs). As for defect, all of investigated Co, Mn and Ge defect show that the spin polarization at Ef and the TMR in the MTJs with Co and Mn defect is significatively decreased except for Ge-defected MTJs.

Nonlinear Structural and Magnetic Transition in Co-Doped Fe2VGa Heusler Alloy

By using local spin density approximation (LSDA) scheme within the density functional theory (DFT), the structural, magnetic and electronic properties of Heusler alloy Fe2V1-xCoxGa were comprehensively investigated. The results reveal that with the increase of Co-doped concentration, in Fe2V1-xCoxGa alloy, a nonmagnetic-ferromagnetic transition appears, and the nonlinearly structural and magnetic variation respectively against the linear Vegard law and Slater-Pauling rule are also detected. Further analysis of electronic structure reveals that both contributions from Fe-Co and Fe-V magnetic interaction in Fe2V1-xCoxGa alloy play a dominating role in determining the nonlinear magnetic and electronic behaviors.

Ion-Electron Interaction Contribution to the Helmholtz Free Energy for Fully Ionized Hydrogen Plasma

The Padé approximation is a very important description of thermodynamic properties of fully ionized hydrogen at high pressures and temperatures. By comparing of several reported Padé approximants via calculation of the ion-electron interaction contribution to the Helmholtz free energy of the fully ionized hydrogen plasma, we find that Padé approximant proposed by Stolzman gives an unphysical odd local minimal appears at low temperature( ), and gradually fade away with the increase of temperature, implying a prominent limit of low temperature. While Chabrier et al. developed a more reasonable Padé approximant for the contribution of ion-electron interaction on the Helmholtz free energy. Analyses on isotherm curves indicate that the thermodynamic properties of the ion-electron interaction contribution to the Helmholtz free energy described by the revised Padé approximant is very stable at all temperatures and pressures without any unphysical effects at low temperatures.

A Density Functional Theory Study of Gd8O12 Cluster

The spin-polarized generalized gradient approximation to the density functional theory is used to determine the geometries, stability, electronic structures, and magnetic properties of the Gd8O12 cluster. Our work reveals that the ground state configuration of the Gd8O12 cluster is a hexahedral cage structure with Ci symmetry. The electronic and magnetic properties imply that the formations of the ionic bonds between the adjacent Gd and O atoms result in the high stability of the Gd8O12 cluster, which is due to the charge transfers between the Gd 5d, 6s electrons to O 2p orbital. It is also confirmed by the electron densities of HOMO-LUMO states. In addition, the analysis of the magnetic properties implies the total magnetic moments are mostly dominated by the Gd 4f orbital.

Electronic Properties and Magnetic Phase Transition in Half-Heusler Compound Fe1-XCuxMnSb

By using the first-principles calculations within the density functional theory (DFT), we investigate the structure, antiferromagnetic-ferromagnetic phase transition and half-metallicity of half-Heusler compound Fe1-XCuxMnSb. For the ferromagnetic state, the calculated lattice constant follows the Vegard law, and total ferromagnetic moment agrees with Slater-Pauling rule as x<0.5 while suffers large deviation as x>0.5. As x=0.75, a novel magnetic phase transition occurs, which mainly derives from the competition between RKKY and superexchange magnetic coupling. Further analyses on density of states (DOS) reveal that the Fermi level can be adjusted by doped Cu concentration in ferromagnetic state, and d partial DOS of Mn atoms with different spin orientation compensate for each other that results in symmetric spin-up and spin-down band in antiferromagnetic state.