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1.
《Journal of magnetism and magnetic materials》1986,62(1):36-46
Magnetic properties of colloidal suspensions of γ-Fe2O3 particles, obtained through a chemical synthesis, are investigated. Using an optical technique it is verified that these ionic aqueous ferrofluids are stable in high fields. The magnetization saturation of the particles is found independent of their size. Electron microscopy, magnetization and birefringence measurements allow us to separate the two superparamagnetic processes existing in such ferrofluid solutions: Bulk and Néel rotations. The Néel process is investigated through remanent magnetization of frozen solution. 相似文献
2.
Jian Li Yueqiang Lin Xiaodong Liu Qingmei Zhang Hua Miao Jun Fu Lihua Lin 《Optics Communications》2012,285(13-14):3111-3115
In binary ferrofluids composed of ferromagnetic γ?Fe2O3/Ni2O3 composite nanoparticles (A particles) and noncrystalline Fe2O3 nanoparticles (B particles), the A particles alone will form chain-like aggregates upon application of a magnetic field. Due to both the long-range ‘magnetic convergent force’ (FC) and the short-range ‘magnetic divergent force’ (FD), the A-particle chains immersed in the B-particle ‘sea’ will move in a manner similar to the process of vibrational damping. The apparent damping of the ferrofluids will vary from weak to overdamping according to the motion of the chains, so that the intensity of light transmitted through a ferrofluid film along the direction of the field would tend to stabilize after a period of rapid decrements and increments. In binary ferrofluids, the B-particle system can produce a modulation effect on both the damping and the driving force, further stabilizing the behavior of the transmitted light. At low fields (e.g., 500 Gs, 900 Gs) only the modulation of the viscosity drag force (Fv) is considerable, so that overdamping increases linearly with B-particle volume fraction (ФB), and the variation in the transmitted light is much slower during the process tending towards stability as ФB increases. However, at high fields (e.g., 1300 Gs) the polarization of the B-particle ‘sea’ is enhanced, so that FD is modulated as well as Fv (i.e., both the practical damping and driving forces are modulated simultaneously). Thus, the apparent overdamping of the binary ferrofluids system will vary non-linearly as ФB increases, and the transmitted light will tend to stabilize faster for ferrofluids with high ΦB than for those with low ФB at an applied magnetic field of 1300 Gs. 相似文献
3.
S. Masoud Hosseini E. Ghasemi H. Ahmadi Moghaddam 《Journal of magnetism and magnetic materials》2010,322(23):3792-3796
A stable γ-Fe2O3 paraffin-based ferrofluid was prepared via high energy milling. The magnetic particles were characterized using X-ray diffraction, dynamic light scattering and vibrating sample magnetometer techniques. The rheological properties of the ferrofluid were studied using a standard rotating rheometer. The magnetoviscous effect and thixotropy in the ferrofluid were studied. The formation and destruction of magnetically induced structures and the interactions of nanoparticles and aggregates are discussed. 相似文献
4.
Shaona Han Jian Li Rongli Gao Tingzhen Zhang Bangcai Wen 《Applied Physics A: Materials Science & Processing》2010,98(1):179-186
The magnetization curves of CoFe2O4 ferrofluids, p-NiFe2O4 paramagnetic fluids and CoFe2O4–p-NiFe2O4 binary ferrofluids, in which the volume fraction of CoFe2O4 particles φ
Co is 0.6% and one of p-NiFe2O4 particles φ
Ni is 0.2%, 0.4%, 0.6% and 0.8% respectively, prepared by the Massart method, have been measured at room temperature. Comparison
of the experimental data from the CoFe2O4 ferrofluids with the Langevin theory curves demonstrates a considerable difference between them, but a curve fitted using
a model of a gas-like compression (MGC) agrees with the experimental data very well. The experimental results show that the
magnetization of the CoFe2O4–p-NiFe2O4 binary ferrofluid is not a simple summation of the ferrimagnetic CoFe2O4 part and the paramagnetic p-NiFe2O4 part. From the fitted results, it was found that the saturation magnetization of the CoFe2O4 part of the binary ferrofluid depends non-monotonically on the p-NiFe2O4 particle volume fraction, and the CoFe2O4 part is a stronger “hard” magnet than CoFe2O4 in simple ferrofluids. The magnetization behavior of the binary ferrofluids is explained by the modification of the microstructure
of CoFe2O4 nanoparticle system by the p-NiFe2O4 nanoparticle system. 相似文献
5.
G. C. Papaefthymiou I. Rabias M. Fardis E. Devlin N. Boukos D. Tsitrouli G. Papavassiliou 《Hyperfine Interactions》2009,190(1-3):59-66
Biomedical applications of magnetic nanoparticles depend critically on their preparation as aqueous colloidal suspensions, or ferrofluids, with long term stability under physiological conditions. Dispersion of the magnetic nanoparticles is generally achieved by the use of protein cages, polysaccharide, polypeptide and charged macromolecular coatings, which minimize interparticle magnetic interactions, particle agglomeration and precipitation. The synthesis and characterization of gummic-acid stabilized maghemite ferrofluids is reported. X-ray diffraction, transmission electron microscope and dynamic light scattering measurements give a γ-Fe2O3 magnetic core diameter of 8 nm and a nanocomposite particle hydrodynamic diameter of 50 nm. Mössbauer and magnetization measurements indicate the presence of isolated, sterically stabilized superparamagnetic nanoparticles resistant to aging, and thus, promising agents for the production of novel magneto-pharmaceuticals. 相似文献
6.
XRD and XPS analyses revealed that a Fe(NO3)3·9H2O layer formed outside γ-Fe2O3 particles when Fe3O4 nanoparticles were treated with ferric nitrate. The particle density differed for untreated and treated particles and was not uniform for the latter. The specific saturation magnetization of both treated and untreated particles was used to estimate the thickness of the Fe(NO3)3·9H2O layer and the average density of the treated particles. The density of the treated particles was used to calculate the density of ferrofluids of different particle volume fractions. These values are in agreement with measured results. Therefore, the particle volume fraction can be designed to synthesize acid ionic ferrofluids based on Fe3O4 nanoparticles using Massart's method. 相似文献
7.
J.E. Knowles 《Journal of magnetism and magnetic materials》1981,22(3):263-266
It is known that acicular particles, initially of Fe3O4, which have been partially oxidised, show anomalous properties e.g. in the variation of Hc with composition. It is shown that these can be explained by considering the particles to comprise an inner core of Fe3O4 with an outer layer of γ-Fe2O3. Owing to the large change in volume which occurs on oxidation, these mutually stress each other. Over a certain range of composition, the stress field interacts with the magnetization to increase Hc, and it is also responsible for Hc increasing with time after the oxidation process. A similar situation applies to partially reduced γ-Fe2O3. 相似文献
8.
A novel magnetic nanocomposite of γ-Fe2O3 nanoparticles decorated multiwalls carbon nanotubes (MWNTs) was synthesized for the first time by a simple chemistry precipitation method. The structure and morphology of the composite was characterized by X-ray powder diffractometer (XRD), TEM and EDS. The results of XRD and TEM show that γ-Fe2O3 nanoparticles is immobilized on the side wall of the MWNTs, the size of most of the particle is <5 nm.The EDS analysis shows that the atomic ratio of Fe to O is 2:3. The magnetization curves of the MWNTs and γ-Fe2O3 decorated MWNTs were measured by VSM at room temperature, which indicate that the saturated magnetization (Ms), remanence (Mr) and coercivity (Hc) of the decorated MWNTs are much larger than those of MWNTs, and the decorated MWNTs exhibit well magnetic properties. 相似文献
9.
测量了MnFe2O4纳米微粒及其磁性液体在室温下的磁化曲线.微粒的中值粒径为13.67 nm. 磁性液体的比饱和磁化强度小于理论值.在高场范围(5~10 kOe)下,磁性液体趋于饱和时,其体积分数越大,磁化曲线的斜率越大. 这种饱和磁化强度性质和趋饱和律分别源自于无场时的环状自组装团聚体和场致团聚体. 场致团聚体是耗散结构,以致于其趋饱和磁化律不同于顺磁理论所描述的趋饱和律. 磁性液体中的大微粒导致了表观磁滞现象. 相似文献
10.
Mikio Kishimoto Makoto MinagawaHideto Yanagihara Tatsuya OdaNobuhiro Ohkochi Eiji Kita 《Journal of magnetism and magnetic materials》2012,324(7):1285-1289
Platelet γ-Fe2O3 particles of particle size less than 100 nm were prepared for medical applications that use the hysteresis-loss heating of ferromagnetic particles. The γ-Fe2O3 particles were obtained through the dehydration, reduction, and oxidation of platelet α-FeOOH particles, which were synthesized by the precipitation of ferric ions in an alkaline solution containing ethanolamine, and the crystals grown using a hydrothermal treatment. The γ-Fe2O3 particles contained dimples formed by the dehydration of α-FeOOH particles. The coercive force and the saturation magnetization of the γ-Fe2O3 particles were in the ranges 11.9 to 12.7 kA/m (150 to 160 Oe), and 70 to 72 Am2/kg (70 to 72 emu/g), respectively. The specific loss power of the γ-Fe2O3 particles, estimated from their temperature-raising property measured under a peak magnetic field of 50.9 kA/m (640 Oe) and at a frequency of 117 kHz, was 590 W/g. This value is higher than that of spherical cobalt-containing iron oxide particles having equivalent coercive force and saturation magnetization, reflecting the larger area of the minor hysteresis loop measured under a peak magnetic field of 50.9 kA/m (640 Oe). 相似文献
11.
Xiaoyan Qiu Zhenghong He Hong Mao Ting Zhang Yueqiang Lin Xiaodong Liu Decai Li Xiangshen Meng Jian Li 《The European Physical Journal B - Condensed Matter and Complex Systems》2017,90(11):227
Using a chemically induced transition method in FeCl2 solution, γ-Fe2O3 based magnetic nanoparticles, in which γ-Fe2O3 crystallites were coated with FeCl3?6H2O, were prepared. During the synthesis of the γ-Fe2O3 nanoparticles Cu(I) modification of the particles was attempted. According to the results from both magnetization measurements and structural characterization, it was judged that a magnetic silent “dead layer”, which can be attributed to spin disorder in the surface of the γ-Fe2O3 crystallites due to breaking of the crystal symmetry, existed in the unmodified particles. For the Cu(I)-modified sample, the CuCl thin layer on the γ-Fe2O3 crystallites incurred the crystal symmetry to reduce the spin disorder, which “awakened” the “dead layer” on the surface of the γ-Fe2O3 crystallites, enhancing the apparent magnetization of the Cu(I)-modified nanoparticles. It was determined that the surface spin disorder of the magnetic crystallite could be related to the coating layer on the crystallite, and can be modified by altering the coating layer to enhance the effective magnetization of the magnetic nanoparticles. 相似文献
12.
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
13.
Nanocrystalline ?-Fe3?x Ni x N (0.0?≤?×?≤?0.8) particles are synthesized by precursor technique and nitridation of decomposed products in NH3 (g) in the temperature range 673 K-823 K. For x?=?0.1–0.4 compositions, single phase ?-Fe3?x Ni x N hexagonal structure with space group P63/mmc is formed, while for x?=?0.5–0.8, fcc γ′-Fe4?y Ni y N phase is also precipitated. The room temperature Mössbauer spectrum for all the compositions shows the presence of superparamagnetic doublet, which is attributed to ?-Fe3?x Ni x N phase. For x?=?0.5–0.8 compositions, two additional sextets are observed corresponding to two different iron sites, the corner position (Fec) and the fcc position (Fef), in γ′-Fe4?y Ni y N. The added Ni atoms preferentially substitute the corner Fec positions. The isomer shift, quadrupole splitting and hyperfine field values are found to change with the Ni content. 相似文献
14.
Kenji Sumiya Tsunetaka Matsumoto Seiji Watatani Fumttada Hayama 《Journal of Physics and Chemistry of Solids》1979,40(12):1097-1102
Highly coercive magnetic powder was obtained by growing cobalt ferrite on the surface of γ-Fe2O3 particles in highly alkaline suspensions containing cobalt and ferrous ions in a Co/Fe molar ratio = . The mechanism of the growth and the structure of cobalt ferrite on γ-Fe2O3 were studied by X-ray diffraction and electron diffraction techniques. Results show that crystals of cobalt ferrite CoFe2O4 with a spinel type crystal structure of lattice constant 8.415 Å grew epitaxially on γ-Fe2O3. The acicular direction of the epitaxially grown Co-γ-Fe2O3 as well as γ-Fe2O3 was in the [01] direction. It was found that from the lattice constant value and the half width of X-ray diffraction peaks, the lattice constant epitaxially grown Co γ-Fe2O3 may be attributed to two kinds of crystals, viz., seed γ-Fe2O3 () which was partly reduced to Fe3O4, and surface layer CoFe2O4 (). The crystal growth in the interface between the seed crystals and the growth layer was affected by the crystal structure of the seed crystals. The lattice constant of CoFe2O4 which was located in the vicinity of the interface was almost equal to that of the seed crystals. 相似文献
15.
16.
Hongyang Zhu Yanzhang Ma Haibin Yang Dongbin Hou 《Journal of Physics and Chemistry of Solids》2010,71(8):1183-9232
Phase transition and bulk moduli of bulk and nanocrystalline γ-Fe2O3 were studied using synchrotron X-ray diffraction under high pressure. Contrary to most other nanomaterials, nanocrystalline γ-Fe2O3 begins to transform into α-Fe2O3 at the same pressure as bulk γ-Fe2O3, which is caused by a special structure of γ-Fe2O3, in which there exist vacancies of crystal. It is believed that phase transition starts from a certain site of vacancy because of the stress concentration at vacancy sites. Compared to bulk material, nanocrystalline γ-Fe2O3 has a larger bulk modulus, which is ascribed to the large ratio of surface to volume. 相似文献
17.
T. I. Krasnenko N. A. Zhuravlev M. V. Rotermel 《Bulletin of the Russian Academy of Sciences: Physics》2013,77(3):246-248
The thermal expansion of Mn2V2O7 in the temperature range of ?190 to 1030°C is studied. The volumetric thermal expansion coefficients for triclinic (α) and monoclinic (β) modifications are 2.57 × 10?5 and 3.86 × 10?5 1/deg, respectively. It is shown that as the Ni2+ concentration in Mn2?2x Ni2x V2O7 rises, the point of the α → β phase transition point moves from room temperature for Mn2V2O7 to 155 ° 5°C for Mn1.46Ni0.54V2O7 (27 mol % Ni2V2O7). 相似文献
18.
Magnetic Behaviour and Heating Effect of Fe3O4 Ferrofluids Composed of Monodisperse Nanoparticles
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Fe3O4 ferrofluids containing monodisperse Fe3O4 nanoparticles with different diameters of 8, 12, 16 and 18nm are prepared by using high-temperature solution phase reaction. The particles have single crystal structures with narrow size distributions. At room temperature, the 8-nm ferrofluid shows superparamagnetic behaviour, whereas the others display hysteresis properties and the coercivity increases with the increasing particle size. The spin glass-like behaviour and cusps near 190K are observed on all ferrofluids according to the temperature variation of field-cooled (FC) and zero-field-cooled (ZFC) magnetization measurements. The cusps are found to be associated with the freezing point of the solvent. As a comparison, the ferrofluids are dried and the FC and ZFC magnetization curves of powdery samples are also investigated. It is found that the blocking temperatures for the powdery samples are higher than those for their corresponding ferrofluids. Moreover, the size dependent heating effect of the ferrofluids is also investigated in ac magnetic field with a frequency of 55 kHz and amplitude of 200 Oe. 相似文献
19.
Zhongzhu Wang Hong Bi Jian Liu Tao Sun Xianliang Wu 《Journal of magnetism and magnetic materials》2008
The conducting protonated polyaniline (ES)/γ-Fe2O3 nanocomposite with the different γ-Fe2O3 content were synthesized by in-situ polymerization. Its morphology, microstructure, DC conductivity and magnetic properties of samples were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), four-wire-technique, and vibrating sample magnetometer (VSM), respectively. The microwave absorbing properties of the nanocomposite powders dispersing in wax coating with the coating thickness of 2 mm were investigated using a vector network analyzers in the frequency range of 7–18 GHz. The pure ES has shown the absorption band with a maximum absorption at approximately 16 GHz and a width (defined as frequency difference between points where the absorption is more than 8 dB) of 3.24 GHz, when 10% γ-Fe2O3 by weight is incorporated , the width is broadened to 4.13 GHz and some other absorption bands appear in the range of 7–13 GHz. The parameter dielectric loss tan δe (=ε″/ε′) in the 7–18 GHz is found to decrease with increasing γ-Fe2O3 contents with 10%, 20%, 30%, respectively, but magnetic loss tan δm (=μ″/μ′) increases with increasing γ-Fe2O3 contents. The results show that moderate content of γ-Fe2O3 nanoparticles embedded in protonated polyaniline matrix may create advanced microwave absorption properties due to simultaneous adjusting of dielectric loss and magnetic loss. 相似文献
20.
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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