The critical properties of the mixed manganite La0.67–x Y x Ba0.23Ca0.1Mn O3 with x=0.10 and x=0.15 around the paramagnetic(PM)-ferromagnetic(FM) phase transition were investigated through various techniques. These i...The critical properties of the mixed manganite La0.67–x Y x Ba0.23Ca0.1Mn O3 with x=0.10 and x=0.15 around the paramagnetic(PM)-ferromagnetic(FM) phase transition were investigated through various techniques. These involved modified Arrott plots, Kouvel-Fisher method and Widom scaling relation. Magnetic data, analyzed in the critical region, using the above methods, yielded the critical exponents for(x=0.10) La0.57Y0.10Ba0.23Ca0.1Mn O3(β=0.312±0.002 and γ=1.147±0.003 at T C=299.23±0.05 K). Moreover, the estimated critical exponents of(x=0.15) La0.52Y0.15Ba0.23Ca0.1Mn O3 were β=0.286±0.004 and γ=0.943±0.002 at T C=289.53±0.06 K. The critical exponents’ values were close to the theoretical values of 3D-Ising model and tricritical mean-field model. These results suggested that the present composition should be close to a tricritical point in the La0.67–x Y x Ba0.23Ca0.1Mn O3 phase diagram. Expressing the field dependence as ΔS M∝H n allowed us to establish a relationship between the exponent n and the critical exponents of the material and to propose a phenomenological universal curve for the field dependence of ΔS M.展开更多
Crystal structure, magnetic properties and magnetocaloric effects(MCE) of La1–xBixFe11.4Si1.6(x=0.0 and 0.1) compounds were investigated by X-ray diffraction and magnetization measurements. The La1–xBixFe11.4Si1.6 c...Crystal structure, magnetic properties and magnetocaloric effects(MCE) of La1–xBixFe11.4Si1.6(x=0.0 and 0.1) compounds were investigated by X-ray diffraction and magnetization measurements. The La1–xBixFe11.4Si1.6 compounds presented a cubic Na Zn13 type structure. First, the magnetization behavior and the magnetic transition were analyzed in terms of Landau theory. Then, Bi substitution for La in La1–xBixFe11.4Si1.6 compounds led to a decrease in magnetic entropy change(-ΔSmaxM) but an increase in Curie temperature(TC) significantly. The significant increase of TC by Bi substitution from 202.5 to 256 K for x=0.0 and x=0.1 respectively was attributed to an increase in the Fe-Fe exchange interactions. Moreover, magnetocaloric effect was calculated in terms of isothermal magnetic entropy change. The maximum values of(-ΔSmaxM) of La1–xBixFe11.4Si1.6 for x=0.0 and 0.1 compounds were found to be, respectively, 22.56 and 4.36 J/(kg·K) under an applied magnetic field change of 5 T. For the same applied magnetic field(μ0H=5 T), the relative cooling power(RCP) values were found to vary between 487 and 296 J/kg.展开更多
La0.67–xDyxPb0.33MnO3(x=0.00 and x=0.10) were elaborated by the solid state method and checked by X-ray diffraction. Close to magnetic temperature transition, the order transition and the critical behavior were inves...La0.67–xDyxPb0.33MnO3(x=0.00 and x=0.10) were elaborated by the solid state method and checked by X-ray diffraction. Close to magnetic temperature transition, the order transition and the critical behavior were investigated by dc magnetization measurements versus x composition. The critical properties were investigated through various techniques such as modified Arrott plot(MAP), Kouvel-Fisher(KF) method and critical isotherm(CI) analysis based on the data of static magnetic measurements recorded around the Curie temperature TC. The values of critical exponents(β and γ) estimated were found to lie between those predicted for a 3D-Ising model for x=0.00 and those of 3D-Heisenberg model for x=0.10. The reliability of the critical exponent's values was confirmed by the Widom scaling relation and the universal scaling hypothesis. The change in the universality class should be due to the increase of the Dy content.展开更多
<正>Self-consistent ab initio calculations,based on the density functional theory(DFT) and using the full potential linear augmented plane wave(FLAPW) method,are performed to investigate both electronic and magn...<正>Self-consistent ab initio calculations,based on the density functional theory(DFT) and using the full potential linear augmented plane wave(FLAPW) method,are performed to investigate both electronic and magnetic properties of the MnS layers.Polarized spin and spin-orbit coupling are included in the calculations within the framework of the antiferromagnetic state between two adjacent Mn layers.Magnetic moments considered to lie along axes are computed. Obtained data from ab initio calculations are used as input data for the high temperature series expansion(HTSE) calculations to compute other magnetic parameters.The zero-field high temperature static susceptibility series of the spin-4.39 nearest-neighbour Heisenberg model on centred face cubic(FCC) and lattices is thoroughly analysed by a power series coherent anomaly method(CAM).The exchange interactions between the magnetic atoms,the Neel temperature,and the critical exponent associated with the magnetic susceptibility are obtained for the MnS layer.展开更多
In this work, the hydrogen storage properties of the Mg-based hydrides, i.e., Mg 1 x M x H 2 (M=Ti, V, Fe, 0 ≤ x ≤ 0.1), are studied using the Korringa-Kohn-Rostoker (KKR) calculation with the coherent potential app...In this work, the hydrogen storage properties of the Mg-based hydrides, i.e., Mg 1 x M x H 2 (M=Ti, V, Fe, 0 ≤ x ≤ 0.1), are studied using the Korringa-Kohn-Rostoker (KKR) calculation with the coherent potential approximation (CPA) . In particular, the nature and concentrations of the alloying elements and their effects are studied. Moreover, the material’s stability and hydrogen storage thermodynamic properties are discussed. In particular, we find that the stability and the temperature of desorption decrease without significantly affecting the storage capacities.展开更多
Electronic and magnetic structures of zinc blende ZnO doped with V impurities are studied by first-principles calculations based on the Korringa-Kohn-Rostoker (KKR) method combined with the coherent potential approxim...Electronic and magnetic structures of zinc blende ZnO doped with V impurities are studied by first-principles calculations based on the Korringa-Kohn-Rostoker (KKR) method combined with the coherent potential approximation (CPA).Calculations for the substitution of O by N or P are performed and the magnetic moment is found to be sensitive to the N or P content.Furthermore,the system exhibits a half-metallic band structure accompanied by the broadening of vanadium bands.The mechanism responsible for ferromagnetism is also discussed and the stability of the ferromagnetic state compared with that of the paramagnetic state is systematically investigated by calculating the total energy difference between them by using supercell method.展开更多
In this work, the hydrogen storage properties of the Mg-based hydrides, i.e., Mg 1 x M x H 2 (M=Ti, V, Fe, 0 ≤ x ≤ 0.1), are studied using the Korringa-Kohn-Rostoker (KKR) calculation with the coherent potential ap... In this work, the hydrogen storage properties of the Mg-based hydrides, i.e., Mg 1 x M x H 2 (M=Ti, V, Fe, 0 ≤ x ≤ 0.1), are studied using the Korringa-Kohn-Rostoker (KKR) calculation with the coherent potential approximation (CPA) . In particular, the nature and concentrations of the alloying elements and their effects are studied. Moreover, the material’s stability and hydrogen storage thermodynamic properties are discussed. In particular, we find that the stability and the temperature of desorption decrease without significantly affecting the storage capacities.展开更多
文摘The critical properties of the mixed manganite La0.67–x Y x Ba0.23Ca0.1Mn O3 with x=0.10 and x=0.15 around the paramagnetic(PM)-ferromagnetic(FM) phase transition were investigated through various techniques. These involved modified Arrott plots, Kouvel-Fisher method and Widom scaling relation. Magnetic data, analyzed in the critical region, using the above methods, yielded the critical exponents for(x=0.10) La0.57Y0.10Ba0.23Ca0.1Mn O3(β=0.312±0.002 and γ=1.147±0.003 at T C=299.23±0.05 K). Moreover, the estimated critical exponents of(x=0.15) La0.52Y0.15Ba0.23Ca0.1Mn O3 were β=0.286±0.004 and γ=0.943±0.002 at T C=289.53±0.06 K. The critical exponents’ values were close to the theoretical values of 3D-Ising model and tricritical mean-field model. These results suggested that the present composition should be close to a tricritical point in the La0.67–x Y x Ba0.23Ca0.1Mn O3 phase diagram. Expressing the field dependence as ΔS M∝H n allowed us to establish a relationship between the exponent n and the critical exponents of the material and to propose a phenomenological universal curve for the field dependence of ΔS M.
文摘Crystal structure, magnetic properties and magnetocaloric effects(MCE) of La1–xBixFe11.4Si1.6(x=0.0 and 0.1) compounds were investigated by X-ray diffraction and magnetization measurements. The La1–xBixFe11.4Si1.6 compounds presented a cubic Na Zn13 type structure. First, the magnetization behavior and the magnetic transition were analyzed in terms of Landau theory. Then, Bi substitution for La in La1–xBixFe11.4Si1.6 compounds led to a decrease in magnetic entropy change(-ΔSmaxM) but an increase in Curie temperature(TC) significantly. The significant increase of TC by Bi substitution from 202.5 to 256 K for x=0.0 and x=0.1 respectively was attributed to an increase in the Fe-Fe exchange interactions. Moreover, magnetocaloric effect was calculated in terms of isothermal magnetic entropy change. The maximum values of(-ΔSmaxM) of La1–xBixFe11.4Si1.6 for x=0.0 and 0.1 compounds were found to be, respectively, 22.56 and 4.36 J/(kg·K) under an applied magnetic field change of 5 T. For the same applied magnetic field(μ0H=5 T), the relative cooling power(RCP) values were found to vary between 487 and 296 J/kg.
文摘La0.67–xDyxPb0.33MnO3(x=0.00 and x=0.10) were elaborated by the solid state method and checked by X-ray diffraction. Close to magnetic temperature transition, the order transition and the critical behavior were investigated by dc magnetization measurements versus x composition. The critical properties were investigated through various techniques such as modified Arrott plot(MAP), Kouvel-Fisher(KF) method and critical isotherm(CI) analysis based on the data of static magnetic measurements recorded around the Curie temperature TC. The values of critical exponents(β and γ) estimated were found to lie between those predicted for a 3D-Ising model for x=0.00 and those of 3D-Heisenberg model for x=0.10. The reliability of the critical exponent's values was confirmed by the Widom scaling relation and the universal scaling hypothesis. The change in the universality class should be due to the increase of the Dy content.
文摘<正>Self-consistent ab initio calculations,based on the density functional theory(DFT) and using the full potential linear augmented plane wave(FLAPW) method,are performed to investigate both electronic and magnetic properties of the MnS layers.Polarized spin and spin-orbit coupling are included in the calculations within the framework of the antiferromagnetic state between two adjacent Mn layers.Magnetic moments considered to lie along axes are computed. Obtained data from ab initio calculations are used as input data for the high temperature series expansion(HTSE) calculations to compute other magnetic parameters.The zero-field high temperature static susceptibility series of the spin-4.39 nearest-neighbour Heisenberg model on centred face cubic(FCC) and lattices is thoroughly analysed by a power series coherent anomaly method(CAM).The exchange interactions between the magnetic atoms,the Neel temperature,and the critical exponent associated with the magnetic susceptibility are obtained for the MnS layer.
文摘In this work, the hydrogen storage properties of the Mg-based hydrides, i.e., Mg 1 x M x H 2 (M=Ti, V, Fe, 0 ≤ x ≤ 0.1), are studied using the Korringa-Kohn-Rostoker (KKR) calculation with the coherent potential approximation (CPA) . In particular, the nature and concentrations of the alloying elements and their effects are studied. Moreover, the material’s stability and hydrogen storage thermodynamic properties are discussed. In particular, we find that the stability and the temperature of desorption decrease without significantly affecting the storage capacities.
文摘Electronic and magnetic structures of zinc blende ZnO doped with V impurities are studied by first-principles calculations based on the Korringa-Kohn-Rostoker (KKR) method combined with the coherent potential approximation (CPA).Calculations for the substitution of O by N or P are performed and the magnetic moment is found to be sensitive to the N or P content.Furthermore,the system exhibits a half-metallic band structure accompanied by the broadening of vanadium bands.The mechanism responsible for ferromagnetism is also discussed and the stability of the ferromagnetic state compared with that of the paramagnetic state is systematically investigated by calculating the total energy difference between them by using supercell method.
文摘 In this work, the hydrogen storage properties of the Mg-based hydrides, i.e., Mg 1 x M x H 2 (M=Ti, V, Fe, 0 ≤ x ≤ 0.1), are studied using the Korringa-Kohn-Rostoker (KKR) calculation with the coherent potential approximation (CPA) . In particular, the nature and concentrations of the alloying elements and their effects are studied. Moreover, the material’s stability and hydrogen storage thermodynamic properties are discussed. In particular, we find that the stability and the temperature of desorption decrease without significantly affecting the storage capacities.