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 i...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 the calculations of lattice parameters, density of states, band gap, local magnetic moment, and the Neel temperature 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.展开更多
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 L...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.展开更多
The perovskite oxide La_ 1-xSr_xCoO_3 ( 0≤x≤0.5) series were prepared under different sintering conditions. Crystal structure was determined by powder X-ray diffraction and lattice parameters as a function of Sr-con...The perovskite oxide La_ 1-xSr_xCoO_3 ( 0≤x≤0.5) series were prepared under different sintering conditions. Crystal structure was determined by powder X-ray diffraction and lattice parameters as a function of Sr-concentration x were obtained by using Rietveld method. The dc resistivity investigated in the temperature range of 80～300 K indicates that the electric properties exhibit a metallic-insulator (semiconducting) (M-I) transition for 0.2<x<0.3. The samples with x=0.2 is close to the M-I transition boundary. The influence of sintering conditions on the lattice parameters, resistivity and the ferromagnetic phase transition temperature T_C of La_ 1-xSr_xCoO_3 for the cases x=0.2 and 0.5 was discussed. The change of the electric properties of semiconductor-like sample (x=0.2) with sintering temperature and sintering period is just opposite to that of metallic sample (x=0.5). Annealing in flowing oxygen can decrease the resistivity of semiconductor-like sample.展开更多
Temperature-dependent resistivity and magnetic susceptibility were studied for quaternary borocarbide intermetallic compounds Y1-xHoxNi2B2C （x = 0, 0.25, 0.5, 0. 75）, which show coexistence of superconductivity with...Temperature-dependent resistivity and magnetic susceptibility were studied for quaternary borocarbide intermetallic compounds Y1-xHoxNi2B2C （x = 0, 0.25, 0.5, 0. 75）, which show coexistence of superconductivity with magnetism. In a normal state, the compounds exhibit conventional metallic behaviour. The Debye temperature θD is derived by fitting the temperature dependence of resistivity to the Bloch-Gruneisen expression, i.e. θD scales with M^-0.5 （M is the averaged atomic mass on the Y^3＋ site）, which means that the acoustic mode of the lattice vibrating spectrum is influenced by the Y^3＋ site atoms. Fitting the temperature-dependent magnetic susceptibility above TN to the Curie-Weiss law, effective magnetic moment μeff is deduced, and then de Gennes factor dG is calculated. It is found that as Ho content increases, μeff as well as dG increases and Tc decreases. Moreover, the decrease of Tc scales with dG, i.e., △Te ∝ -nI^2 N （EF ）dG, which is consistent with the prediction of the Abrikosov-Gor＇kov theory. We suggest that pair-breaking effect of magnetic Ho^3＋ ions. The significant impact on To. the depression of Tc could be mainly ascribed to the magnetic change of Debye temperature with Ho content may not have significant impact on Tc.展开更多
Temperature dependence of the upper critical magnetic field （Hc2） near Tc of 20 K in a BaFe1.9 Ni0.1 As2 single crystal is determined via magneto-resistance measurements, for the out-plane （H ⊥ab） and in-plane ...Temperature dependence of the upper critical magnetic field （Hc2） near Tc of 20 K in a BaFe1.9 Ni0.1 As2 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^｜｜12（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-x Cox As2, indicating that electron-doped 122 superconductors exhibit similar superconducting properties.展开更多
Two SiO_2/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 d...Two SiO_2/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 SiO_2/Si interface structure described by DBM leads to a larger gate leakage current.展开更多
文摘基于脉冲激光沉积(PLD)技术在光寻址电位传感器(LAPS)表面上制备了Fe-Ge-Sb-Se硫系玻璃薄膜,合成的靶材成分为Fe1.2(Ge28Sb12Se60)98.8,在Si/SiO2基质上的金属层为Cr/Au,硫系玻璃薄膜对Fe3+敏感,显示了良好的重复性和稳定性.在1×10-5～1×10-2mol/L呈现线性,斜率为(56±2)mV/decade,检测下限为5×10mol/L,当浓度高于1×10-4mol/L时,响应时间不超过40 s;当低于此浓度时,响应时间不超过2 min.
基金Project supported by the Qianjiang Talent Project of Zhejiang Province, China (Grant No 2007R10028)the National Natural Science Foundation of China (Grant No 50802089)+2 种基金the Opening Project of State Key Laboratory of High Performance Ceramicsand Superfine Microstructure, China (Grant No SKL200805SIC)the Scientific Research Foundation for the Returned Overseas Chinese Scholars,Ministry of Education of China (Grant No [2008] 890)Natural Science Foundation of Zhejiang Province,China (Grant No Y407188)
文摘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 the calculations of lattice parameters, density of states, band gap, local magnetic moment, and the Neel temperature 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.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51072183 and 50802089)the Natural Science Foundation of Zhejiang Province,China(Grant No.Y4090280)
文摘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.
文摘The perovskite oxide La_ 1-xSr_xCoO_3 ( 0≤x≤0.5) series were prepared under different sintering conditions. Crystal structure was determined by powder X-ray diffraction and lattice parameters as a function of Sr-concentration x were obtained by using Rietveld method. The dc resistivity investigated in the temperature range of 80～300 K indicates that the electric properties exhibit a metallic-insulator (semiconducting) (M-I) transition for 0.2<x<0.3. The samples with x=0.2 is close to the M-I transition boundary. The influence of sintering conditions on the lattice parameters, resistivity and the ferromagnetic phase transition temperature T_C of La_ 1-xSr_xCoO_3 for the cases x=0.2 and 0.5 was discussed. The change of the electric properties of semiconductor-like sample (x=0.2) with sintering temperature and sintering period is just opposite to that of metallic sample (x=0.5). Annealing in flowing oxygen can decrease the resistivity of semiconductor-like sample.
基金Supported by the National Natural Science Foundation of China under Grant No 10225417, and National Basic Research Programme of China under Grant No 2006CB601003.
文摘Temperature-dependent resistivity and magnetic susceptibility were studied for quaternary borocarbide intermetallic compounds Y1-xHoxNi2B2C （x = 0, 0.25, 0.5, 0. 75）, which show coexistence of superconductivity with magnetism. In a normal state, the compounds exhibit conventional metallic behaviour. The Debye temperature θD is derived by fitting the temperature dependence of resistivity to the Bloch-Gruneisen expression, i.e. θD scales with M^-0.5 （M is the averaged atomic mass on the Y^3＋ site）, which means that the acoustic mode of the lattice vibrating spectrum is influenced by the Y^3＋ site atoms. Fitting the temperature-dependent magnetic susceptibility above TN to the Curie-Weiss law, effective magnetic moment μeff is deduced, and then de Gennes factor dG is calculated. It is found that as Ho content increases, μeff as well as dG increases and Tc decreases. Moreover, the decrease of Tc scales with dG, i.e., △Te ∝ -nI^2 N （EF ）dG, which is consistent with the prediction of the Abrikosov-Gor＇kov theory. We suggest that pair-breaking effect of magnetic Ho^3＋ ions. The significant impact on To. the depression of Tc could be mainly ascribed to the magnetic change of Debye temperature with Ho content may not have significant impact on Tc.
基金Supported by the National Basic Research Program of China under Grant No 2006CB601003, and the National Science Foundation of China under Grant No 10634030.
文摘Temperature dependence of the upper critical magnetic field （Hc2） near Tc of 20 K in a BaFe1.9 Ni0.1 As2 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^｜｜12（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-x Cox As2, indicating that electron-doped 122 superconductors exhibit similar superconducting properties.
文摘Two SiO_2/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 SiO_2/Si interface structure described by DBM leads to a larger gate leakage current.
