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991.
Xuezhi Zhou Wanjun JiangHenry Kunkel Gwyn Williams 《Journal of magnetism and magnetic materials》2008
A summary of the results of ac susceptibility and isothermal magnetization measurements on polycrystalline samples of Ce2Fe17−xSix with nominal composition of x=0.0, 0.1, 0.2 and 1.0 is presented. These data reveal that the substitution of small amounts of Si for Fe produce a significant increase in temperature at which ferromagnetism appears, to the extent that, at x=1, characteristics of the anti ferromagnetic to paramagnetic transition (at temperature TN) have disappeared completely. The nature of the various magnetic phase transitions — identified through the use of Arrott plots — and the accompanying magnetic entropy change, ΔSm, are both affected significantly by small amounts of Si substitution. In particular, while the peak entropy change is modest (occurring at x=0.1), the temperature interval over which a substantial entropy change occures is significant, approaching 150 K, an important criterion for improving the overall effectiveness of such materials for magnetic refrigeration. 相似文献
992.
D.M. Rajkumar M. Manivel RajaR. Gopalan V. Chandrasekaran 《Journal of magnetism and magnetic materials》2008
Evolution of structure and magnetocaloric properties in ball-milled Gd5Si2Ge2 and Gd5Si2Ge2/0.1 wt% Fe nanostructured powders were investigated. The high-energy ball-milled powders were composed of very fine grains (70–80 nm). Magnetization decreased with milling time due to decrease in the grain size and randomization of the magnetic moments at the surface. The magnetic entropy change (ΔSM) was calculated from the isothermal magnetization curves and a maximum value of 0.45 J/kg K was obtained for 32 h milled Gd5Si2Ge2 alloy powder for a magnetic field change of 2 T while it was still low in Fe-contained alloy powders. The thermo-magnetic measurements revealed that the milled powders display distribution of magnetic transitions, which is desirable for practical magnetic refrigerant to cover a wide temperature span. 相似文献
993.
We comment on both recent progress and lingering puzzles related to research on magnetic tunnel junctions (MTJs). MTJs are already being used in applications such as magnetic-field sensors in the read heads of disk drives, and they may also be the first device geometry in which spin-torque effects are applied to manipulate magnetic dynamics, in order to make non-volatile magnetic random access memory. However, there remain many unanswered questions about such basic properties as the magnetoresistance of MTJs, how their properties change as a function of tunnel-barrier thickness and applied bias, and what are the magnitude and direction of the spin-transfer-torque vector induced by a tunnel current. 相似文献
994.
Chengyong Liu Zhongwen LanXiaona Jiang Zhong YuKe Sun Lezhong LiPeiyuan Liu 《Journal of magnetism and magnetic materials》2008
The effects of sintering temperature and Bi2O3 content on the microstructure and magnetic properties of lithium–zinc (LiZn) ferrites prepared by a conventional ceramic method were investigated. The results show that the densification behavior and grain growth rate were greatly improved by the addition of Bi2O3, because a liquid phase sintering occurred during the sintering process at high temperature due to the low-melting point of Bi2O3 (825 °C). X-ray diffraction (XRD) patterns of the slightly doped samples did not reveal the appearance of any phase other than spinel LiZn ferrite. However, the secondary phase of perovskite BiFeO3 was detected for Bi2O3 content of more than 0.25 wt%. The studies further show that Bi oxide was present at grain boundary, and promoted the grain growth as reaction center at lower temperature. A high saturation magnetization, squareness ratio, minimum ferromagnetic resonance linewidth and low coercive force were obtained for the sample with 1.00 wt% Bi2O additive at lower sintering temperature (1100 °C). 相似文献
995.
S.Y. Li B.W. Wang L. Weng Y. Zhou Y. Sun W.M. Huang 《Journal of magnetism and magnetic materials》2008
Based on the analysis of the magnetostriction for Terfenol-D composites, Terfenol-D 2-2 magnetostrictive composites have been prepared with laminations perpendicular to [1 1 2] axes. Then one of the samples was annealed in the vacuum at 423 K for 15 min at the magnetic field of 240 kA/m, which is along the direction of laminations and vertical to the [1 1 2] axes of the specimen. The static magnetostriction λ and dynamic magnetostrictive coefficient d33 of samples were measured under the compressive stress of 0, 2, 4, 6 and 8 MPa. Effects of the compressive stress and the magnetic field heat treatment on the magnetostriction λ have been investigated. It is found that the magnetostriction of 2-2 composites can be improved under the compressive stress when the magnetic field is larger than 20 kA/m. The magnetostriction of 2-2 composites with the magnetic field heat treatment increases under compressive stress, and it can reach 1390×10−6 at the magnetic field of 200 kA/m and under the compressive stress of 4 MPa, much larger than the value of 860×10−6 without the magnetic field heat treatment. The highest magnetostriction of the 2-2 composite with the magnetic field heat treatment can reach 1530×10−6. The dynamic magnetostrictive coefficient d33 of 2-2 composites with the magnetic field heat treatment have been improved, compared with that without magnetic field heat treatment. The maximum value of d33 of the sample with magnetic field heat treatment is 71% larger than that without magnetic field heat treatment. 相似文献
996.
Kh. Gheisari S. JavadpourH. Shokrollahi B. Hashemi 《Journal of magnetism and magnetic materials》2008
Ferromagnetic powders which are surrounded by an electrically insulating film (soft magnetic composites (SMCs)) exhibit unique magnetic properties, such as relatively low magnetic losses and 3D isotropic magnetic behavior. In some electromagnetic applications, including microwave frequency range applications, it is necessary to increase electrical resistivity without any noticeable reduction in magnetic properties. To achieve this purpose, electrically resistant materials, for example, ferrites with acceptable magnetic properties, are suitable candidates. This paper focuses on the effects of the synthesized Ni–Zn ferrite addition on the magnetic properties of the SMCs containing Ni–Zn ferrite within iron particles. The structure was studied by means of X-ray diffraction (XRD). The microstructure and the powder morphology were examined by the use of scanning electron microscopy (SEM). The magnetic measurements on powders and samples were carried out using a vibrating sample magnetometer (VSM) and an LCR meter, respectively. The results indicate that the lowest magnetic loss and the highest magnetic permeability are related to the composites with 20 wt% ferrite and 2 wt% ferrite, respectively. Also, the composites with 10 wt% ferrite show a good combination of magnetic loss and magnetic permeability in the range 0–500 kHz. 相似文献
997.
Preparation of nanocrystalline Fe–Ni powders by mechanical alloying used in soft magnetic composites
R. Koohkan S. Sharafi H. Shokrollahi K. Janghorban 《Journal of magnetism and magnetic materials》2008
This paper focuses on the preparation of nanocrystalline Fe–Ni powders by mechanical alloying method, which can be used in soft magnetic composites. Fe–10 wt% Ni and Fe–20 wt % Ni alloys were prepared using a high-energy ball mill. The magnetic properties of samples were measured by a B–H curve analyzer and microstructures of the samples were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The bcc Fe(Ni) phase formation was identified by XRD and completed after 45 h of milling. It was found that higher milling time resulted in, larger lattice parameter, higher microstrains and smaller crystallite sizes. Also, results showed that with increasing the milling time, coercivity increased and saturation intrinsic flux density firstly increased noticeably and then decreased in higher milling times (>70 h). 相似文献
998.
The effects of annealing temperature and manganese substitution on the formation, microstructure and magnetic properties of MnxZn1−xFe2O4 (with x varying from 0.3 to 0.9) through a solid-state method have been investigated. The correlation of the microstructure and the grain size with the magnetic properties of Mn–Zn ferrite powders was also reported. X-ray diffraction (XRD), a scanning electron microscope (SEM) and a vibrating sample magnetometer (VSM) were utilized in order to study the effect of variation of manganese substitution and its impact on crystal structure, crystalline size, microstructure and magnetic properties of the ferrite powders formed. The XRD analysis showed that pure single phases of Mn–Zn ferrites were obtained by increasing the annealing temperature to 1200–1300 °C. Increasing the annealing temperature to ?1300 °C led to abnormal grain growth with inter-granular pores and this led to a decrease in the saturation magnetization. Moreover, an increase in the Mn2+ ion substitution up to x=0.8 increased the lattice parameter of the formed powders due to the high ionic radii of the Mn2+ ion. Mn–Zn ferrites phases were formed and the positions of peaks were shifted by substituting manganese. The average crystalline size was increased by increasing the annealing temperature and decreased by increasing the substitution by manganese up to 0.8. The average crystalline size was in the range 95–137.3 nm. The saturation magnetization of the Mn–Zn-substituted ferrite powders increased continuously with an increase in the Mn concentration up to 0.8 at annealing temperatures of 1200–1300 °C. Further increase of Mn substitution up to 0.9 led to a decrease of saturation magnetization. The saturation magnetization increased from 17.3 emu/g for the Mn0.3Zn0.7Fe2O4 phase particles produced to 59.08 emu/g for Mn0.8Mn0.2Fe2O4 particles. 相似文献
999.
J. Pérez P.J. Silva C.A. Durante-Rincón J. Primera Ferrer J.R. Fermin 《Journal of magnetism and magnetic materials》2008
Electron paramagnetic resonance (EPR) experiments were made in the diluted magnetic semiconductor CuGa1−xMnxTe2, in the temperature range 70<T<300 K. The samples were synthesized by direct fusion of stoichiometric mixtures of the elements, with Mn composition from x=0.0 to 0.25. The EPR spectra were measured as function of temperature, Mn composition, and field orientation. The temperature variation of the resonance field shows a critical point at about 235 K, and is associated with a transition from the ferromagnetic to the superparamagnetic state. The resonance field was also measured as a function of the field angle, and displays a well-defined uniaxial symmetry. This uniaxial field depends on the Mn concentration and is due to tetragonal distortions induced by Mn2+ at Ga sites, and the demagnetizing effects due to formation of ferromagnetism (FM) Mn-clusters. 相似文献
1000.
Nanostructured Pr8Fe86−xVxB6−yCy (x=0, 1; y=0, 1) ribbons composed of Pr2Fe14B and α-Fe phases with a high coercivity are fabricated by direct melt spinning. The effects of a single addition of V and a combined addition of V and C on the structures and magnetic properties of melt-spun Pr8Fe86VB6−xCx (x=0 and 1) ribbons have been investigated. Compared with addition-free ribbons, 1 at% V addition is found to reduce the grain sizes of the samples and improve their magnetic properties due to a strong exchange coupling between the hard and the soft phase. A remanence ratio of 0.82, a coercive field of 6.2 kOe and a maximum energy product of 23.4 MGOe in melt-spun Pr8Fe85VB6 ribbons are obtained at room temperature. The combined addition of V and C is found to lead to the formation of an intermediate phase of VC at grain boundaries, which appears as a pinning barrier during magnetization and results in an increase of the coercivity value to 6.9 kOe for melt-spun Pr8Fe85VB5C ribbons. 相似文献