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包钴型γ-Fe2O3磁粉的矫顽力可比原γ-Fe2O3磁粉提高8000—32000A/m。木文研究探讨了两种包钴型γ-Fe2O3磁粉(包钴γ-Fe2O3和包钴包亚铁γ-Fe2O3)的单轴各向异性的起源和矫顽力增大的机制。包钴γ-Fe2O3磁粉矫顽力
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包钴铁氧体型,γ-Fe2O3磁粉(简记为CoFe-γ-Fe2O3)是针状γ-Fe2O3磁粉与Co++和Fe++溶液起反应,在每个针状颗粒上包覆了一层钴铁氧体固溶体。经此种方法处理后的γ-Fe2O3磁粉的矫顽力及其它磁特性有较大的提高。如矫顽力由原来415Oe增加到715Oe;剩磁和矫顽力随时间及温度变化小等。我们利用穆斯堡尔效应并配合其它研究手段进行了研究,认为:CoFe-γ-Fe2O3磁粉矫顽力的提高,主要是由于γ-Fe2O3磁粉表面包覆了一层钴铁氧体固溶体,γ-Fe2O3与钴铁氧体固溶体之间发生磁耦合作用之故。
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为了改善永磁薄膜的磁性能,基于微磁学理论,使用编程软件OOMMF针对Ce1.66Mg1.34Co3和α″-Fe16N2交换耦合多层梯度膜的磁化过程进行模拟,系统研究磁晶各向异性梯度对多层膜性能的影响,分析体系的剩余磁化强度、矫顽力、磁滞回线和磁化反转过程中的能量变化。研究表明:减小磁晶各向异性梯度或增加界面处磁晶各向异性的差值,可以有效提高薄膜的矫顽力和剩余磁化强度,从而改善磁性能。通过计算磁矩分布发现一种磁涡旋态,这种磁涡旋态的产生过程伴随系统能量的增加。 相似文献
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磁性Fe3O4纳米粒子在纳米医学领域展现出巨大的应用前景.饱和磁化强度和磁各向异性对于Fe3O4纳米粒子在药物输送和磁热疗中的应用至关重要.在此,通过密度泛函理论计算,仔细研究了3d和4d过渡金属元素的掺杂对Fe3O4磁矩及磁各向异性的影响.结果表明, Fe3O4中Zn和Cd的掺杂会增大总磁矩,而其他3d和4d过渡金属元素的掺杂会降低总磁矩.有趣的是, Cd的掺杂也会大大增大磁各向异性.本文结果表明,掺杂Cd是提高Fe3O4作为药物输送和磁热疗材料性能的可行方法. 相似文献
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铁质文物是我国文化遗产的重要组成部分。由于化学性质较为活泼,铁质文物易发生腐蚀劣化。锈蚀产物对铁质文物的稳定性有较大影响,因此判断铁质文物锈蚀产物的组成特征,对于铁质文物稳定性评估具有重要意义。以赤铁矿(α-Fe2O3),磁铁矿(Fe3O4),四方纤铁矿(β-FeOOH)三种铁质文物的锈蚀产物为研究对象,采用拉曼光谱成像结合主成分回归法(PCR)和偏最小二乘法(PLS),同时结合多种预处理方法,构建了两组二元混合锈蚀(α-Fe2O3+Fe3O4, α-Fe2O3+β-FeOOH)的定量模型。结果表明,对于α-Fe2O3+Fe3O4二元体系,PCR和PLS算法构建模型的定量效果基本一致,α-Fe2O3和Fe3O... 相似文献
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Toshihide Tsuji Yoshikazu Mochida Keiji Naito Koji Shibuya 《Hyperfine Interactions》1992,68(1-4):287-290
The effects of calcium and zinc on the room-temperature coercivity of γ-Fe2O3 particles having cobalt ions adsorbed in 3M NaOH solution at 373K have been studied. When the Ca2+ ions are adsorbed on the γ-Fe2O3 prior to Co2+ ions adsorption, the coercivity of Co-modified γ-Fe2O3 significantly increases compared with that of γ-Fe2O3 modified only with Co2+ ions. In the case of Zn2+ ions, the coercivity of Co-modified γ-Fe2O3 is the same as that of γ-Fe2O3 modified only with Co2+ ions. The emission Mössbauer spectrum of57Co2+ adsorbed on the surfaces of γ-Fe2O3 after pretreating with Ca2+ ions consists of a typical sextet of Fe3+ ions with hyperfine magnetic field, whereas those of γ-Fe2O3 modified only with Co2+ ions and with both Zn2+ and Co2+ ions show nonmagnetic components in addition to magnetic one. The effects of Ca2+ and Zn2+ ions on the adsorption of cobalt on the surface of γ-Fe2O3 are discussed from the viewpoint of site preference energy of cations in ferrite and distribution ratio of each cation. 相似文献
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The (γ′-Fe4N/Si-N)n (n: number of layers) multilayer films and γ′-Fe4N single layer film synthesized on Si (1 0 0) substrates by direct current magnetron sputtering were annealed at different temperatures. The structures and magnetic properties of as-deposited films and films annealed at different temperatures were characterized using X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer. The results showed that the insertion of Si-N layer had a significant influence on the structures and magnetic properties of γ′-Fe4N film. Without the addition of Si-N lamination, the iron nitride γ′-Fe4N tended to transform to α-Fe when annealed at the temperatures over 300 °C. However, the phase transition from γ′-Fe4N to ?-Fe3N occurred at annealing temperature of 300 °C for the multilayer films. Furthermore, with increasing annealing temperature up to 400 °C or above, ?-Fe3N transformed back into γ′-Fe4N. The magnetic investigations indicated that coercivity of magnetic phase γ′-Fe4N for as-deposited films decreased from 152 Oe (for single layer) to 57.23 Oe with increasing n up to 30. For the annealed multilayer films, the coercivity values decreased with increasing annealing temperature, except that the film annealed at 300 °C due to the appearance of phase ?-Fe3N. 相似文献
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I.V. VasylenkoS.V. Kolotilov I.E. KotenkoK.S. Gavrilenko F. TunaG.A. Timсo R.E.P. WinpennyV.V. Pavlishchuk 《Journal of magnetism and magnetic materials》2012,324(4):595-601
Thermal decomposition of the trinuclear complex [Fe2CrO(CH3COO)6(H2O)3]NO3 at 300, 400 and 500 °C gave γ-Fe2O3 nanoparticles along with amorphous chromium oxide, while decomposition of the same starting compound at 600 and 700 °C led to the formation of α-(Fe2/3Cr1/3)2O3 nanoparticles. Size of γ-Fe2O3 nanoparticles, determined by X-ray diffraction, was in the range from 9 to 11 nm and increased with formation temperature growth. Average size of α-(Fe2/3Cr1/3)2O3 nanoparticles was about 40 nm and almost did not depend on the temperature of its formation. γ-Fe2O3 nanoparticles possessed superparamagnetic behavior with blocking temperature 180-250 K, saturation magnetization 29-35 emu/g at 5 K, 44-49 emu/g at 300 K and coercivity 400-600 Oe at 5 K. α-(Fe2/3Cr1/3)2O3 nanoparticles were characterized by low magnetization values (2.7 emu/g at 70 kOe). Such magnetic properties can be caused by non-compensated spins and defects present on the surface of these nanoparticles. The increase of α-(Fe2/3Cr1/3)2O3 formation temperature led to decrease of magnetization (being compared for the same fields), which may be caused by decrease of the quantity of defects or non-compensated spins (due to decrease of particles' surface). 相似文献
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包钴型γ-Fe2O3磁粉分为包钴γ-Fe2O3(简记为Co-γ-Fe2O3)和包钴包亚铁γ-Fe2O3(简记为CoFe-γ-Fe2O3)两种,它们的矫顽力可比γ-Fe2O3磁粉的提高100至400Oe左右,本工作对这两种磁粉矫顽力增大的原因作了探讨,认为它们矫顽力增大的机制不同:CO-γ-Fe2O3矫顽力增大是由于表面包覆一层Co(OH)2使表面各向异性增大,而CoFe-γ-Fe2O3则是由于表面包覆的是钴铁氧体,γ-Fe2O3与钴铁氧体之间发生耦合作用,使矫顽力增大。 相似文献
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D. Ortega J. S. Garitaonandia M. Ramírez-del-Solar C. Barrera-Solano M. Domínguez 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,52(1-3):19-22
Evolution of static magnetic properties of a set of enhanced γ-Fe2O3/SiO2 nanocomposites with different iron concentration has been studied on the basis of their corresponding hysteresis loops, zero-field/field-cooled (ZFC/FC) magnetization curves and transmission electron microscopy images. The lack of coercivity in all compositions, as well as the fulfillment of the H/T scaling law by the magnetization above the blocking temperature of each system under study, evidence a superparamagnetic behaviour in the iron oxide nanoparticles. In order to study the influence of iron content in the unblocking processes of nanoparticles, ZFC curves under different applied magnetic fields have been fitted to a model considering the systems under study as a distribution of energy barriers. Depart from the superparamagnetic model is discussed considering interparticle interactions. 相似文献
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The 57Fe Mössbauer spectra recorded in situ from tin-doped Fe3O4 at elevated temperature in vacuo shows the Curie temperature to decrease with increasing concentrations of the dopant. Thermal treatment under oxidising conditions results in the initial formation of tin-doped γ-Fe2O3 which subsequently undergoes a phase transformation to tin-doped α-Fe2O3. 57Fe Mössbauer spectroscopy at elevated temperatures shows the Néel temperature for tin-doped γ-Fe2O3 to be lower than that of pure γ-Fe2O3. The 119Sn Mössbauer spectra recorded from all the tin-doped iron oxides show the presence of a hyperfine magnetic field at the Sn4+ site which is more complex in the spectra recorded from tin-doped γ-Fe2O3 and α-Fe2O3. 相似文献
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Yosun HwangS. Angappane Jongnam ParkKwangjin An T. HyeonJe-Geun Park 《Current Applied Physics》2012,12(3):808-811
We have carried out systematic studies on well-characterized monodisperse Fe3O4/γ-Fe2O3 core/shell nanoparticles of 2-30 nm having a very narrow size distribution and possessing a uniquely mono-layer of surface γ-Fe2O3. This unique core-shell structure, probably having a disordered magnetic surface state, leads us to three key observations of unusual magnetic properties: i) a very large magnetic exchange anisotropy reaching over 7 × 106 erg/cm3 for the smaller particles, ii) exchange bias behavior in the magnetization data of the core/shell Fe3O4/γ-Fe2O3 nanoparticles, and iii) the temperature dependence of the coercive field following an unusual exponential behavior. 相似文献
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《Journal of magnetism and magnetic materials》2005,294(3):294-297
Fe2O3–Al2O3 nano-composites were synthesized by sol–gel means. The properties of samples sintered at various thermal treatment temperatures were investigated by X-ray diffraction (XRD) and Mössbauer spectroscopy (MS). The experimental results show that the γ- to α-Al2O3 transformation occurs at lower temperature after iron oxide doping. The samples obtained at 1173 K contained poorly crystallized γ-Al2O3 phase and an amorphous iron oxide. When the temperature of heating was increased to 1373 K, the sample was composed of α-Fe2O3/α-Al2O3 nano-composite and some solid solution. A superparamagnetic phenomenon was observed until the thermal treatment temperature reached 1373 K. 相似文献
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A. G. Savchenko S. V. Salikhov E. V. Yurtov Yu. D. Yagodkin 《Bulletin of the Russian Academy of Sciences: Physics》2013,77(6):704-709
The results of complex structural investigation by XRD, TEM, and Mössbauer spectroscopy of nanomaterials based on iron oxides Fe3O4 and γ-Fe2O3 are presented. The investigated nanomaterials include nanopowders produced chemically and nanostructural powders produced mechanochemically. The magnetic properties of the nanomaterials, measured at ambient temperature, are discussed. 相似文献