Quan-feng Zheng

Electronic structure of MgCNi3−xTMx (TM=Cu,Co,Mn)

The effects on the electronic structure and magnetic property of the Ni site substitution in nonoxide perovskite superconductor MgCNi3 are studied by using density functional calculations. A sharp high peak of Ni d density of states just lies below the Fermi energy in pure MgCNi3. Co-doping results in the onset of ferromagnetism at x=0.083. However, the little energy gain as well as small magnetic moment per atom indicate the weak itinerant ferromagnetism. The strong ferromagnetic spin fluctuation in MgCNi3−xCox leads to quench bulk superconductivity, while the Mn atom forms a local magnetic moment of 1.06 μB at x=0.042 which suppresses superconductivity more seriously than Co does in the low doping case. Cu doping can be well accounted for by the rigid band model, which reduces the density of states at the Fermi level and the Tc.

Electronic structure of heavy fermion superconductor CeMIn5 (M=Co,Rh,Ir)

The electronic structure of heavy fermion superconductor CeMIn5 (M=Co,Rh,Ir) is studied by density functional theory. Our results indicate that the MIn2 layer plays an important role for stabilizing the layered crystal structure and determining the antiferromagnetic or paramagnetic ground state in this series. When the strong correlation effects of 4f electrons beyond the local density approximation (LDA) are taken into account by the LDA+U approach, the calculated total magnetic moment and band structure of CeRhIn5 yield a good agreement with the experiment. The LDA+U calculation shows that the 4f electrons in this series are located on the border between localization and itineracy.

A full electron LMTO‐ASA study of electronic band structure and magnetic properties for RFe11TiNx (R=Y, Nd, Sm; x=0,1)

The band structure and magnetic properties are studied for RFe11TiNx (R=Y, Nd, Sm; x=0,1) rare‐earth iron intermetallic compounds using the linear muffin tin orbital with the atomic sphere approximation (LMTO‐ASA) method. In order to elucidate the role played by the rare‐earth atoms in these compounds, a full electron calculation is performed using a semirelativistic spin‐polarized LMTO‐ASA method in the local spin density approximation (LSDA) regime. The 4f electrons of the rare‐earth atoms are considered to be valence electrons in the self‐consistent calculations. For NdFe11TiN, a calculation in which the 4f electrons are treated as core‐frozen states is also performed, and is compared with the full electron calculation. The effects of N atoms in these compounds are also discussed.

Biostratigraphy constraining strontium isotopic stratigraphy and its application on the Lopingian (Late Permian)

The Lopingian is one of the fastest rising periods of seawater strontium isotopic ratios (87Sr/86Sr) in earth history, and its mechanisms and increasing rates of the 87Sr/86Sr evolution were still disputed widely. These disputations among researchers were caused mainly by timeframe selection (sections’ thickness or data of radiometric ages), and different stratigraphic boundaries and un-upmost dated ages. This paper examined published 87Sr/86Sr data of the Lopingian, and projected them on timescales based on evolutionary and age constrained conodonts fossils. 87Sr/86Sr evolution vs fossil constraining timescales was re-established in this period. This research suggests: (1) 87Sr/86Sr excursion projects on fossil zones can truly support 87Sr/86Sr evolutionary pattern in the period; (2) 87Sr/86Sr evolution provides a new approach for stratigraphic research of marine carbonate sections in lieu of biostratigraphic data; (3) 87Sr/86Sr stratigraphy works on marine carbonate sections of different sedimentation rates even between different basins; (4) the 87Sr/86Sr data and its shift was dependent on samples materials and chemical treatment methods; (5) the increasing rate of marine water 87Sr/86Sr in the Late Permian is suggested as 5.4×10−5/Ma or slightly lower; (6) sedimentation age and its 87Sr/86Sr of the Lopingian marine carbonate suggested as: DPRO=259-(RS−0.70695)/5.4×10−5±1 Ma.

Hydrostatic pressure effect in La1−xCaxMnO3

The pressure effect is studied for the doped compound La1−xCaxMnO3 (x=1/3) using the first-principles spin-polarized discrete variational method, in the framework of density functional theory with local density approximation. The pressure dependence of both effective electron hopping integral t and Hund’s coupling strength JH is investigated systematically, which is essential to explain the qualitative relations between the pressure and properties such as colossal magnetoresistance and the Curie temperature Tc of this material.

Electronic structure study of Nd0.5Ca0.5MnO3 with a charge-exchange-type antiferromagnetic ordering

The electronic structures and magnetic properties of manganites Nd0.5Ca0.5MnO3 with a charge-exchange-type antiferromagnetic ordering are studied by a modified linear combination of the atomic orbital (LCAO) band method within and beyond the local spin density approximation (LSDA and LSDA+U). The known crystal structure with Jahn–Teller distortion is modeled by a large supercell consisting of 80 atoms. Orbital-ordered states like those observed experimentally are obtained in both the LSDA and LSDA+U approaches. However, the LSDA fails in getting the experimentally confirmed charge-ordered insulating ground state. Although the inclusion of the Coulomb interaction, U, in the LSDA+U approach does reduce significantly the density of states of Mn ions around the Fermi level, it does not lead to the formation of an insulating gap. The LSDA+U calculation also shows that with the inclusion of U, the 4f of Nd ions become the majority component of the residual density of states near the Fermi level. In addition, th...