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We report our ab - initio calculational results for the electronic structures and the magnetooptical (MO) properties of the ferromagnetic Co2MnX full Heusler alloys where X = Ge, Sn and Pb. Employing the +U corrections for the 3d bands of transition-metal atoms in addition to the conventional local density approximation (LDA), we investigate the correlation effect on the MO spectra in a polar geometry and the detailed electronic structures. Results show that the correlation effect results in a blue-shift of the peak positions and a large enhancement of the MO spectra up to double in magnitude compared to the LDA results. We find that our results can be attributed to the increased t 2g − e g splitting of the spin-minority d-bands of both Co and Mn atoms, which indicates a suppression of the diagonal elements of the optical conductivity in the energy region of 1–2 eV where the interband transitions are forbidden.

We study the properties of the (001) surfaces of ternary vanadium compounds based on the rocksalt semiconductor GeTe. In one of the compounds 25% of Ge atoms are replaced by V atoms, and in another, the substitution is as large as 50%. Using a first-principles method, we calculate the electronic structure of the two systems for two different surface terminations. The studied systems are found to be half-metallic ferromagnets. The half-metallic gap in every system is found to be larger than it is in the bulk. However, in Ge-terminated surfaces, the bottom of the conduction band is very near the Fermi level, and this may cause an instability of the half-metallicity in the systems. VGe-terminated surfaces are characterized by a more stable half-metallic ferromagnetic order. The larger amount of replacement of Ge atoms by V atoms also supresses the magnetic properties of the system. The largest calculated magnetic moment on the V atom at the topmost layer of the (001) surface is 2.602 µ B . The presence of a magnetic center causes polarization of the metalloids: in the 50%-substituted GeTe, Te atoms are negatively polarized, and Ge atoms are slightly positively polarized. The largest magnetic moment on Te is calculated for Te atom at the topmost layer and is −0.107 µ B .

We report the ab-initio calculational results for the half-metallicity of the Co2FeSi full Heusler alloy in (001) surfaces. Employing the +U corrections, in addition to the local density approximation (LDA) and generalized gradient approximation (GGA), we investigate the effects of surface and correlation interactions on the half-metallicity and the magnetic properties. The (001) surfaces are calculated to be metallic by both the LDA and the GGA due to the surface states the develop at the Fermi energy (EF). Upon +U correction, the surface states are pushed down below EF for the Co-terminated surface, which recovers the half-metallicity with a reduced band gap of 0.40 eV. In contrast, the FeSi-terminated surface is predicted to be metallic because the surface states remain at the Fermi level in spite of an enhanced t2g−eg band splitting caused by the correlation effect.

In this study, we investigated the electronic structure and the magnetism of a system of Co layers grown on a W(001) surface, which exhibited relatively larger exchange splitting compared to that in the bulk in a recent experiment. We used the full-potential linearized augmented plane wave (FLAPW) method based on density functional theory to examine the possibility of formation of a surface alloy. The general gradient approximation was employed to describe the exchangecorrelation potential. In this study, we considered a Co ML on a W(001) surface [1Co/W(001)] and a checkboard type CoW surface alloy on a W(001) surface [1(CoW)/W(001)], and we relaxed the systems by calculating total energies, being guided by the calculated forces. We found from the calculated total energies of the clean W(001) surface, the 1Co/W(001), and the 1(CoW)/W(001) that the surface alloy was favored energetically and that the alloy formation energy was about 380 meV. The ferromagnetic (FM) state was more stable, based on an energy difference of about 28 meV per Co atom, compared to the antiferromagnetic (AFM) one for 1(CoW)/W(001) whereas the AFM state was more favorable, based on an energy difference of about 25 meV per Co atom pair, than the FM one in 1Co/W(001). We will discuss the roles of the band hybridization between Co and W atoms in determining the ground magnetic states from the calculated single-particle energy spectra.

We present the results of the electronic structure calculations for a copper tetraazaporphyrin (CuTAP) model monolayer, both bare and interacting with oxygen. The results are compared with those obtained for copper phthalocyanine. We have found that the CuTAP ferromagnetic configuration is preferred over the paramagnetic one. The calculated value of the magnetic moment of the Cu atom in the CuTAP monolayer is 0.54 µB. It does not aect strongly the magnetic properties of the monolayer, in which all but pyrrole nitrogen atoms remain unpolarized. The presence of oxygen molecules in the vicinity of the metallic center of the CuTAP causes a decrease in the magnetic moment of Cu, but does not much influence the overall magnetic properties of the monolayer. However, it influences slightly the ground-state electronic structure of the monolayer, mainly due to the charge transfer between the tetraazaporphyrin ring and the O2 molecules.

We investigate the magnetic properties of an Fe monolayer residing between two graphene sheets with the use of the full-potential linearized augmented plane wave method within the generalized gradient approximation. We consider three Fe monolayers of di erent morphologies sat in the middle between two C(0001) layers. In the densest monolayer, Fe atoms occupy each hollow position available between C(0001) layers and in the least dense structure, the occupancy is 50 %. The equilibrium interlayer distance is determined through total energy calculations and the electronic and the magnetic properties of the equilibrium structures are discussed. The calculated magnetic moments on Fe atoms are 2.23 B for dense structures and 2.03 B for the structure with the largest interatomic distance. The least dense structure was found to be half-metallic with a total magnetic moment per unit cell of 2.0 B . For this structure, an energy gap is found for the majority spin channel. In the investigated systems, the sp-d hybridization between C and Fe atoms plays an important role and is noticeable in less dense structures. The magnetic properties of an Fe monolayer may be adjusted by controlling both the density of the monolayer and the interlayer distance in the system.

on the magnetism and the electronic structures by using the all-electron total-energy full-potential linearized augmented plane wave (FLAPW) method within the generalized gradient approximation (GGA) for the exchange-correlation potential. We found, from the calculated bond lengths of each atom, that the atomic relaxations tend to smooth the edges with a 100 % contraction of the interlayer distance between the edge atoms. The calculated local magnetic moments depend mostly on the coordination numbers rather than on the interatomic bond lengths. The magnetic moment (M) dependency on the dimensionless geometrical factor x, which is defined by the ratio between the coordination number and the average bond length of a specific atom, is quantitatively analyzed to propose an empirical rule of M / x , where is geometry-dependent exponent. From the calculated density of states, we found that the surface localization eects determine the magnetic moments of the surface atoms, including the edge atoms. However, the geometrical complications of the edge atoms provide the reason for the local magnetic moments of the edge atoms being smaller than those of the terrace atoms.

We calculated the electronic structures of several Co2-based full Heusler compounds with 4d transition elements T and Si, Co2TSi (T = Y, Zr and Nb), by using the all electron full potential band method and found that the Co2ZrSi is half-metallic ferromagnet. The calculated atomic resolved density of states (DOSs) for Co2ZrSi showed that it had a considerably large minority spin gap (0:94 eV) and that the Fermi level was pinned just at the middle of the gap. The fact that the Co2ZrSi had an integer value for the magnetic moment, 2:000 „B per formula unit (f.u.), also indicated that this compound was half-metallic. Calculations for the compounds Co2YSi and Co2NbSi showed that they were not half-metals, but ferromagneic metals with magnetic moments of 1:002 and 2:243 „B/f.u., respectively. The Fermi level of Co2YSi, located at the left edge of the minority spin gap, made the material nearly half-metallic while that of Co2NbSi was positioned just below a large peak of minority Co 3d states.