Shen Jingqin

Structural and magnetic properties of LiNi0.5Mn1.5O4 and LiNi0.5Mn1.5O4−δ spinels: A first-principles study

Structural and magnetic properties of LiNi0.5Mn1.5O4 and LiNi0.5Mn1.5O4−δ are investigated using density-functional theory calculations. Results indicate that nonstoichiometric LiNi0.5Mn1.5O4−δ and stoichiometric LiNi0.5Mn1.5O4 exhibit two different structures, i.e., the face-centred cubic (Fd-3m) and primitive, or simple, cubic (P4332) space groups, respectively. It is found that the magnetic ground state of LiNi0.5Mn1.5O4 (P4332 and Fd-3m) is a ferrimagnetic state in which the Ni and Mn sublattices are ferromagnetically ordered along the [110] direction whereas they are antiferromagnetic with respect to each other. We demonstrate that it is the presence of an O-vacancy in LiNi0.5Mn1.5O4−δ with the Fd-3m space group that results in its superior electronic conductivity compared with LiNi0.5Mn1.5O4 with the P4332 space group.

Theoretical study of the SiO2/Si interface and its effect on energy band profile and MOSFET gate tunneling current

Two SiO2/Si interface structures, which are described by the double bonded model (DBM) and the bridge oxygen model (BOM), have been theoretically studied via first-principle calculations. First-principle simulations demonstrate that the width of the transition region for the interface structure described by DBM is larger than that for the interface structure described by BOM. Such a difference will result in a difference in the gate leakage current. Tunneling current calculation demonstrates that the SiO2/Si interface structure described by DBM leads to a larger gate leakage current.

Upper Critical Fields and Anisotropy of BaFe1.9 Ni0.1As2 Single Crystals

Temperature dependence of the upper critical magnetic field (Hc2) near Tc of 20 K in a BaFe1.9Ni0.1As2 single crystal is determined via magneto-resistance measurements, for the out-plane (H⊥ab) and in-plane (H || ab) directions in magnetic fields of up to 8 T. The upper critical fields at zero temperature estimated by the Werthamer-Helfand-Hohenberg (WHH) formula are μ0H||c2(0) = 137 T and μ0H⊥c2(0) = 51 T, both exceeding the weak-coupling Pauli paramagnetic limit (μ0Hp = 1.84Tc). However, the WHH formula could overestimate the μ0H||c2(0) value. The anisotropy of upper critical fields is around 3 in the temperature range close to Tc. The result is very similar to the Co-doped 122 superconductor BaFe2–xCoxAs2, indicating that electron-doped 122 superconductors exhibit similar superconducting properties.

First-principles investigation of the electronic structure and magnetism of eskolaite

The electronic structure and magnetism of eskolaite are studied by using first-principles calculations where the on-site Coulomb interaction and the exchange interaction are taken into account and the LSDA+U method is used.The calculated energies of magnetic configurations are very well fitted by the Heisenberg Hamiltonian with interactions in five neighbour shells; interaction with two nearest neighbours is found to be dominant. The Neel temperature is calculated in the spin-3/2 pair-cluster approximation. It is found that the measurements are in good agreement with for the values of U and J that are close to those obtained within the constrained occupation method.The band gap is of the Mott-Hubbard type.