Zheng Qing-Qi

Electronic structures and magnetic properties of Fe2P and the effects of doping with Ni

The first-principles self-consistent cluster method has been used to study the electronic structures and magnetic properties of Fe2P and the effect of doping with Ni. We find that, for Fe2P, the local magnetic moments of FeI atoms at the tetrahedral sites are smaller than those of FeII atoms at the pyramidal sites owing to the greater hybridization of FeI with P; when Ni atoms replace FeI atoms, the FeII magnetic moment shows a slight increase and the ferromagnetism of the (Fe1-xNix)2P compounds is strengthened. However, the substitutions of Ni in FeII sites reduce the FeI atom magnetic moment substantially. These results are in good agreement with experiments.

Electronic structure and magnetic properties of MnBi(Al,Nd)

The electronic structure and magnetic properties of MnBiAl and MnBiNd were studied using molecular cluster model within the local density functional approximation. The obtained results of MnBi are in good agreement with ASW and experiments. Influences of Al and Nd impurities were discussed. The Bi 6p band was found much polarized and the magnetic moment decreased by Al and Nd atom which is attributed to the electron transfer between majority band and minority band.

The electronic structure and magnetic behaviour in the Mn-containing cubic Laves-phase pseudobinary compound of YFe2

The fully self-consistent discrete variational method within the local-spin-density framework has been employed to obtain the electronic structure and magnetic moments of the Mn-containing cubic Laves-phase pseudobinary compound of YFe2. The embedded-cluster model was used to simulate the local environments around Fe in this compound. The calculated results show that the substitution of Mn atoms on Fe sites weakens the ferromagnetism of this compound. With the change of the local environments around Fe. We find that when Fe has one or two Mn atoms in its nearest-neighbour sites, its magnetic moment decreases rapidly, while the Mn moment is 071 mu B, parallel to the Fe moment; when Fe has four or more than four Mn atoms in its nearest-neighbour sites, the moments of these Mn atoms are reversed and antiparallel to the Fe moments and meanwhile the Fe moments increase. In addition, calculations for the cluster with an Mn atom occupying a Y site indicates that such an Mn atom is in a high-spin state. Based upon our results, the various experimental data have been satisfactorily explained.

Cluster studies on the electronic and magnetic properties of MnBi and MnBiAl

Abstract The electronic structure and magnetic properties of MnBi and MnBiAl were studied using the molecular cluster model within the local density functional theory. The influence of cluster size on the calculation results is also discussed. We got quite satisfactory results compared with ASW and experiments. Influences of Al impurity were also studied using different Al content and locations. The main effect of doped Al atoms is the polarization of the Bi 6p band and decrease of the magnetic moment of Mn which is attributed to the charge transfer from the majority band to the minority band. The possible reason for the enhancement of the Kerr rotation in MnBiAl is discussed.

The electronic structure of the surface of the superconductor YBa2Cu3O7

The electronic structures of several clusters in different Cu-O planes considered as possible surfaces in the superconductor YBa2Cu3O7 are studied within the framework of local density theory. Self-consistent solutions are obtained using the discrete variational and Xalpha cluster method. Several peaks in the UPS are identified by comparing the calculated values of the density of states with the experimental data. The surface electronic structure of the material is also discussed.

Electronic structure and magnetic properties of R2Fe17N3

Abstract Self-consistent, spin-polarized local spin density functional theory calculations have been performed for Sm 2 Fe 17 N 3 , a new permanent magnetic material. Several cluster models were used to study the electronic structure of this system. The locations of nitrogen atoms was determined by total energy calculation. The s-d (s-f) exchange interaction for different Fe sites and Sm atoms was also evaluated. The role of N atoms in R 2 Fe 17 N 3−δ was discussed.

Size-dependence of the local magnetic moments in finite systems

The size effect on the magnetic and electronic properties of an impurity in finite systems is investigated based on the Anderson admixture model in real space. Within the self-consistent mean field approximation, it is found that the formation of the local magnetic moment strongly depends on the size of finite linear quantum chains up to a few nanometers. The density of states for the local electrons is also obtained.

The influence of Al on the electronic structure and magnetic properties of doped MnBi with huge enhancement of Kerr rotation

Abstract The electronic structure of MnBi alloys doped with Al was studied by means of the cluster model. As compared with the case of pure MnBi, the effect of Al on the density of state near the Fermi surface, the exchange interaction, the spin-orbit coupling and the magnetic moments were evaluated. The results obtained may give an understanding for the mechanism of huge enhancement of Kerr rotation which is observed in MnBi film doped by Al atoms.

The effect on Si on the local magnetic moment and hyperfine interaction of BCC-Fe

The electronic structure and local magnetic properties of disordered Fe-rich Fe-Si alloys were calculated using the first-principles self-consistent cluster method. The calculated local magnetic moment, isomer shift and hyperfine field are compared with the existing experimental results. The Fe 3d magnetic moment was found to decrease with the number of Si atoms appearing in the first and second neighbouring shells. The isomer shift increases and the hyperfine field decreases in magnitude with an increasing number of Si atoms in the cluster.

Effect of sulphur and carbon segregation on chemical bonding of grain boundaries in BCC metal iron

The effect of sulphur and carbon impurity segregation on chemical bonding of grain boundaries for b.c.c. metal iron was investigated using the self-consistent field Xα discrete variational method. A relaxed trigonal-prism cluster was used as one of the structural units of the grain boundaries. The grain boundary embrittlement, which is caused by impurity segregation, is interpreted by the electron charge transfer from neighbouring iron atoms onto impurity atoms, and by the characteristics of empty levels in the energy bands of the segregated grain boundaries.