Abstract: In this paper the perfect Ni2MnGa cluster model is studied by use of the first principles discrete variational method (DVM), which is based on the framework of density- function theory. To study the characteristic properties of the alloy and the influence of the impurities which substitute for Mn at the central, the electronic structure、the binding energy and site energy are calculated. The result illuminates that Ni2MnGa complex obviously has metallic property. Ga plays to transmit electron for the exchange actions between Mn and Mn. And the periodic influence of 11 impurity elements on the binding energy and the site energy is gived. From the microcosmic the reason of the martensitic temperature changed with the concentration of element is analyzed.
Abstract: Giant magnetocaloric effect based on first order phase transformation has been
investigated extensively recently. A considerable magnetic entropy change has been found in single crystal Ni52.6Mn23.1Ga24.3, Ni53Mn22Ga25 and polycrystal Ni51.5Mn22.7Ga25.8.This change originated from a sharp magnetization jump caused by the martensitic-austenitic structure transition on heating. In this paper, magnetocaloric effect in the alloys Ni54.9Mn20.5Ga24.6 is studied. The Curie point
temperature Tc of the alloy is adjusted to the vicinity of martensitic transition temperature Tm. The concurrence of martensitic structure transition and magnetic phase transition enhance the magnetocaloric effect in these alloys. The martensitic structure transition effect on the magnetic properties of the alloys is investigated. The character of magnetocaloric effect during the transition from the austenitic to martensitic state is discussed.
Abstract: In this paper, composites with Tb:Dy ratio of 0.30:0.70 and 0.33:0.67 were fabricated by polymer infiltration method. Both maximum d33 and strain of composites with different Tb/Dy ratio (0.33:0.67, 0.30:0.70) were investigated as a function of the volume fraction of RFe2 phase. The maximum d33 and the strain of composites with higher Tb:Dy ratio (higher magnetocrystalline anisotropy) showed higher than that of composites with lower one as volume fraction of RFe2 increased.
Abstract: The magnetostriction and dynamic characteristics of Tb0.27Dy0.73Fe2 polycrystals with <110> axial alignment were investigated by standard strain gauge, two coil induction and lock-in amplifier techniques. It is found that the magnetostriction of the sample quickly increases with increasing magnetic fields when H≤80 kA/m under a pressure of 5 or 10 MPa and a “jump” effect occurs during the magnetization process. The dynamic strain coefficient, d33, dynamic incremental permeability,μ33, and magneto-mechanical coupling coefficient, k33, for the Tb0.3Dy0.7Fe2 rod polycrystal sample with <110> axial alignment were measured and discussed. The Tb0.27Dy0.73Fe2 polycrystals with <110> axial alignment possesses excellent magnetostrictive properties along the <110> rod direction in low magnetic fields and it is very useful in application of industry.
Abstract: In this work series of models were constructed in order to investigate the relationship between atomic and electronic structure and TMR property. Models with normal component interface of Fe/MgO/Fe magnetic tunnel junctions were calculated by first-principles discrete variational method (DVM) within the framework of local spin density functional theory. The SP and TMR ratio of Fe at interface of ferromagnetic layer as well as density of states are analyzed. Our
research shows that the thickness of ferromagnetic layers effect much on electronic structure. The interface and surface Fe layers have different feature from that of interior.
Abstract: The magnetotransport behaviors of electron-doped colossal magnetoresistance (CMR) manganites La0.9Te0.1MnO3 have been investigated in external magnetic fields up to 4 T. The temperature dependence of the resistivity shows that the transport mechanisms of the sample below the metal-insulator transition temperature are attributed to the electron-phonon and magnon scattering behaviors. While the resistivity above Curie temperature (Tc=240 K) can be fitted with either polaron transport or variable-range hopping, and the fitting results are affected significantly by the magnetic fields. The electron spin resonance investigation indicated that there exist the ferromagnetic clusters up to 280 K in the paramagnetic phase of the sample. As a result, a possible correlation between the resistivty and phase separation is considered.
Abstract: The thin polycrystalline Co films with different annealed time were prepared by
magnetron sputtering method. XRD and hysteresis loops of the samples were measured. A mean field equation with Heisenberg model for calculating dynamic scaling was derived. The experimental and simulated results indicate that, the scaling law, A=A0+H0 a ω b, describes well dynamic magnetization along easy and hard axes for the anisotropy magnetic films; the anisotropy scaling exponents exist clearly in the anisotropy films; the simulated results are consistent with the experimental those.
Abstract: A series of Gd1-xCrx (x=0.01,0.03,0.05 and 0.07) alloys have been prepared by arc melting. After introducing a small quantity of Cr into Gd, the Curie temperatures of these alloys increase. Magnetic entropy changes at the Curie temperature of Gd1-xCrx (x=0.01, 0.03, 0.05) alloys are nearly the same as that of Gd. However, compared with Gd, the magnetic entropy changes of Gd1-xCrx (x=0.01, 0.03, 0.05) alloys remain at a high level in a wider temperature range. So Gd1-xCrx (x=0.01, 0.03, 0.05) alloys are more suitable as magnetic refrigerant to be used in Ericsson Recycle for room temperature magnetic refrigeration. Our results and the fact that Cr is quite cheaper than Gd, suggest that Gd1-xCrx alloys maybe utilized as refrigerant in room temperature magnetic refrigeration.
Abstract: As FeOx particles were prepared by oxidation-reduction reaction, the surfactant of
polyethylene glycol (ab. PEG) was used to cover the FeOx particles, thus the PEG/FeOx ferrofluids were obtained. The morphology, structure and composition of the ferrofluids were investigated. The results show that the product is spheric in the shape, and the diameter of the product is obviously influenced by PEG content and slightly influenced by the stirring rate. When the content of PEG increases in the range of 50～350g/L, the diameter of the product decreases. However, when the content of PEG is in the range of 350～750g/L, the diameter increases with the
increasing of PEG content. When the stirring rate is between 50 and 150r/min, the diameter of the product slightly decreases as the stirring rate increases. Moreover, the results demonstrate that the products are mainly constituted of PEG and FeOx, and the value of x in the formula of FeOx can be adjusted by controlling the molar ratio of H2O2 to Fe2+. Further analysis indicates that the organic and inorganic components of the PEG/FeOx ferrofluids are combined by both physical adsorption and coordinate combination.
Abstract: Fe3O4 nanoparticles were simply prepared by a wet chemical solution method. In this method, poly (N-vinyl-2-pyrrolidone) (PVP) was used as surface modified reagent to control the shape of the product. Transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD) were used to characterize the asprepared Fe3O4 nanoparticles. Furthermore, the magnetic properties of the sample were investigated by a VSM (vibrating sample magnetometer) technique.