共查询到20条相似文献,搜索用时 0 毫秒
1.
《Journal of magnetism and magnetic materials》2001,232(3):181-188
When the thin film of high-quality magnetic fluid is subjected to a perpendicular magnetic field, a separation of particles from the liquid matrix will occur, leading to a phase transition with a phase that is concentrated in particles separating from a dilute phase. The concentrated phase makes up the cylindrical columns that can form two-dimensional lattices. We have explored the field-induced lattices with optical microscopy, digital imaging and computer-video techniques in this study, to classify the ordering property in terms of bond-orientation order. 相似文献
2.
C.N. Marin P.C. FanninI. M?l?escu P. BarvinschiA. Ercu?a 《Journal of magnetism and magnetic materials》2012,324(4):434-439
We report on the frequency and field dependent complex magnetic susceptibility measurements of a kerosene-based magnetic fluid with iron oxide nanoparticles, stabilized with oleic acid, in the frequency range 0.1-6 GHz and over the polarising field range of 0-168.4 kA/m.By increasing polarising field, H, a subsidiary loss-peak clearly occurs in the vicinity of the ferromagnetic resonance peak, from which it remains distinct even in strong polarising fields of 168.4 kA/m. This is in contrast to other reported cases in which the intra-well relaxation process is manifested only as a shoulder of the resonance peak, which vanishes in polarising fields larger than that of 100 kA/m.The results of the XRD analysis connected to the anisotropy field results confirm that the investigated sample contains particles of magnetite and of the tetragonal phase of maghemite.Taking into account the characteristics of our sample, the theoretical analysis revealed that the intra-well relaxation process of the small particles of the tetragonal phase of maghemite may be responsible for the subsidiary loss peak of the investigated magnetic fluid. 相似文献
3.
Y. Sugimoto S. Takaoka K. Oto 《Physica E: Low-dimensional Systems and Nanostructures》2004,22(4):867-871
The cyclotron resonance of two-dimensional electron systems (2DES) of GaAs/AlGaAs heterostructures is investigated in a tilted magnetic field. In this study, the perpendicular (B) and in-plane (B||) magnetic fields are changed systematically. More than two cyclotron resonances caused by B|| are observed. Further, the enhancement of cyclotron mass by B|| and its dependence on B and electron concentration of 2DES are also investigated in detail. These phenomena are well explained by the resonant subband Landau level coupling model. 相似文献
4.
Seiichi Sudo Daisaku AsanoHidemasa Takana Hideya Nishiyama 《Journal of magnetism and magnetic materials》2011,323(10):1314-1318
The dynamic behavior of a magnetic fluid adsorbed to a small NdFeB permanent magnet subjected to an alternating magnetic field was studied with a high speed video camera system. The directions of alternating magnetic field are parallel and opposite to that of the permanent magnet. It was found that the surface of magnetic fluid responds to the external alternating magnetic field in elongation and contraction with a lot of spikes. Generation of a capillary magnetic fluid jet was observed in the neighbourhood of a specific frequency of alternating field. The effect of gravitational force on surface phenomena of magnetic fluid adsorbed to the permanent magnet was revealed. 相似文献
5.
A.F. Pshenichnikov 《Journal of magnetism and magnetic materials》2012,324(7):1342-1347
A new algorithm for calculating magnetic fields in a concentrated magnetic fluid with inhomogeneous density is proposed. Inhomogeneity of the fluid is caused by magnetophoresis. In this case, the diffusion and magnetostatic parts of the problem are tightly linked together and are solved jointly. The dynamic diffusion equation is solved by the finite volume method and, to calculate the magnetic field inside the fluid, an iterative process is performed in parallel. The solution to the problem is sought in Cartesian coordinates, and the computational domain is decomposed into rectangular elements. This technique eliminates the need to solve the related boundary-value problem for magnetic fields, accelerates computations and eliminates the error caused by the finite sizes of the outer region. Formulas describing the contribution of the rectangular element to the field intensity in the case of a plane problem are given. Magnetic and concentration fields inside the magnetic fluid filling a rectangular cavity generated under the action of the uniform external filed are calculated. 相似文献
6.
K.-F. Braun S. Sievers M. Albrecht U. Siegner K. Landfester V. Holzapfel 《Journal of magnetism and magnetic materials》2009,321(22):3719-3725
We investigate the effect of external magnetic fields on the magnetic structure of thin films from magnetic nanoparticles (MNP) with dipolar interaction. Such fields are present, for example, if samples are scanned with magnetic probes. Numerical simulations and experimental magnetic force microscopy (MFM) studies are presented. Numerically, we have calculated the magnetization pattern of single-layer and multilayer MNP thin films. The calculations show that unperturbed single-layer MNP films have an in-plane orientation of the magnetization with a flux-closure-domain pattern. An external field generated by a point dipole above the film induces locally an out-of-plane configuration of the magnetization. In the corresponding MFM images, the domain pattern in the film is erased and a stripe-like contrast enhancement at the edges appears. Multilayer films are found to be more robust against external fields than monolayers. 相似文献
7.
Magnetic field induced first order antiferromagnetic (AFM) to ferrimagnetic (FRI) transition in polycrystalline Mn1.85Co0.15Sb has been studied using magnetic force microscopy (MFM) at 60 K and up to 8 T magnetic fields. Our MFM studies provide real space visualization of AFM to FRI transition. It shows growth (decay) of FRI phase with increasing (decreasing) magnetic field. The hysteretic behavior and co-existing FRI and AFM phases across the critical field required for FRI-AFM transition in Mn1.85Co0.15Sb are highlighted. This study demonstrates the potential of MFM for studying phase co-existence at high field and low temperatures. 相似文献
8.
A.T. Asvini meenaatci R. RajeswarapalanichamyK. Iyakutti 《Physica B: Condensed Matter》2011,406(13):2610-2615
First principles calculation was performed using tight-binding LMTO method with local density approximation (LDA) and atomic sphere approximation (ASA) to understand the electronic properties of chromium nitride. The equilibrium geometries, the magnetic moment, the electronic band structure, the total and partial DOS are obtained under various pressures and are analyzed in comparison with the available experimental data. The most stable structure of CrN is NaCl structure in the FM state. A pressure-induced second order magnetic phase transition from ferromagnetic (FM) to non-magnetic (NM) at very high pressure of 0.5549 Mbar is predicted. Our results indicate that CrN can be used as a hydrogen storage material. 相似文献
9.
Marcela Gonzales-Weimuller Kannan M. Krishnan 《Journal of magnetism and magnetic materials》2009,321(13):1947-1950
Using the thermal decomposition of organometallics method we have synthesized high-quality, iron oxide nanoparticles of tailorable size up to ∼15 nm and transferred them to a water phase by coating with a biocompatible polymer. The magnetic behavior of these particles was measured and fit to a log-normal distribution using the Chantrell method and their polydispersity was confirmed to be very narrow. By performing calorimetry measurements with these monodisperse particles we have unambiguously demonstrated, for the first time, that at a given frequency, heating rates of superparamagnetic particles are dependent on particle size, in agreement with earlier theoretical predictions. 相似文献
10.
ESR spectra of a laboratory synthesized kerosene base magnetic fluid containing ultrafine magnetic particles (average diameter
of 100A) of Zn0.1 Fe0.9Fe2O4 are recorded at different temperatures. A narrow signal was observed above the melting point of the carrier liquid (200 K)
which can be attributed to a very small volume fraction of superparamagnetic particles in the system. The peak-to-peak line
width for both low and high field cooled configurations show an increase with decreasing temperature. This observed behaviour
has been explained by considering various energy terms which contribute to the line width. 相似文献
11.
This paper presents acoustic properties of water-based biocompatible fluids in which magnetite particles (Fe3O4) were coated with two layers of surfactants: sodium oleate and dextran. The attenuation coefficient of ultrasonic wave measurements shows good structural stability of the fluid under the influence of a magnetic field. Hyperthermic tests proved that the magnetic fluid is suitable for therapeutic use as an agent which can release thermal energy (hyperthermia). 相似文献
12.
Digital imaging is used to study the particle positions and trajectories of a layer of highly charged 0.3 μm diameter polystyrene spheres in water suspension, rigidly confined into two-dimensions between two smooth glass plates. As the in-plane sphere density is varied, we find a two-stage melting transition in which we observe separate divergences in the orientational and translational order at different densities, separated by roughly 4%. The topological defect statistics are complex, but qualitatively consistent with the predictions of Halperin and Nelson. 相似文献
13.
T.I. Ivanova S.A. Nikitin A. Gilewski 《Journal of magnetism and magnetic materials》2010,322(13):1741-1743
Magnetization isotherms for polycrystalline TbMnGe and DyMnGe compounds were measured at the temperature 4.2 K in pulsed magnetic fields (up to 360 kOe). The received isotherms demonstrate the appearance of metamagnetic transitions at low temperatures. Both compounds crystallize in the orthorhombic TiNiSi-type structure. It was found that the magnetic phase transitions with a destruction of ferrimagnetic spiral structure occur in the TbMnGe and DyMnGe compounds in high magnetic fields. An attempt was undertaken to explain the nature of these transitions using the results of the powder neutron diffraction and the qualitative estimation of the exchange interaction values on the basis of the molecular field theory. 相似文献
14.
Teppei KikuchiRyo Kasuya Shota EndoAkira Nakamura Toshiyuki TakaiNils Metzler-Nolte Kazuyuki TohjiJeyadevan Balachandran 《Journal of magnetism and magnetic materials》2011,323(10):1216-1222
An aqueous magnetic suspension was prepared by dispersing amphiphilic co-polymer-coated monodispersed magnetite nanoparticles synthesized through thermal decomposition of iron acetylacetonate (Fe(acac)3) in a mixture of oleic acid and oleylamine. The average diameter of narrow-size-distributed magnetite nanoparticles varied between 5 and 12 nm depending on the experimental parameters such as reaction temperature, metal salt concentration and oleic acid/oleylamine ratio. Though the as-synthesized particles were coated with oleate and were dispersible in organic solvent, their surfaces were modified using amphiphilic co-polymers composed of poly(maleic anhydride-alt-1-octadecene) and polyethylene glycol-methyl ether and made dispersible in water. Infrared spectra of the sample indicated the existence of −COOH groups on the surface for further conjugation with biomolecules for targeted cancer therapy. 相似文献
15.
The relaxation behavior (including the rising and falling relaxation processes) of the transmitted light after the magnetic fluid thin films under longitudinal and transverse magnetic fields is investigated, respectively. The physical mechanisms of the two different relaxation processes are discussed. The experimental data of the rising and falling relaxation processes are fitted by using two exponential functions to achieve the rising and falling response times. The relationship between the response time and the strength of applied magnetic field, the concentration of magnetic fluid is studied experimentally. The modulation depth of the transmitted light is researched quantificationally and the deepest modulation depth is obtained with Sample 3 (with volume fraction of 5.62%) in our experiments. 相似文献
16.
Very promising nanoparticles for biomedical applications or in medical drug targeting are superparamagnetic nanoparticles based on a core consisting of iron oxides (SPION) that can be targeted through external magnets. Polyvinyl alcohol (PVA) is a unique synthetic biocompatible polymer that can be chemically cross-linked to form a gel. Biotechnology applications of magnetic gels include biosensors, targeted drug delivery, artificial muscles and magnetic buckles. These gels are produced by incorporating magnetic materials in the polymer composites. In this paper we report the synthesis of an aqueous ferrofluid and the preparation of a biocompatible magnetic gel with polyvinyl alcohol and glutharaldehyde (GTA). HClO4 was used to induce the peptization since this kind of ferrofluid does not have surfactant. The magnetic gel was dried to generate a biocompatible film. 相似文献
17.
Y.M. WangX. Cao G.H. LiuR.Y. Hong Y.M. ChenX.F. Chen H.Z. LiB. Xu D.G. Wei 《Journal of magnetism and magnetic materials》2011,323(23):2953-2959
Fe3O4 magnetic nanoparticles were prepared by co-precipitation from FeSO4·7H2O and FeCl3·6H2O aqueous solutions using NaOH as precipitating reagent. The nanoparticles have an average size of 12 nm and exhibit superparamagnetism at room temperature. The nanoparticles were used to prepare a water-based magnetic fluid using oleic acid and Tween 80 as surfactants. The stability and magnetic properties of the magnetic fluid were characterized by Gouy magnetic balance. The experimental results imply that the hydrophilic block of Tween 80 can make the Fe3O4 nanoparticles suspending in water stable even after dilution and autoclaving. The magnetic fluid demonstrates excellent stability and fast magneto-temperature response, which can be used both in magnetic resonance imaging and magnetic fluid hyperthermia. 相似文献
18.
Osman O. Ahsen M. Deniz Aksoy Ergin Atalar 《Journal of magnetism and magnetic materials》2010,322(20):3053-3059
A theory is presented to calculate the heat dissipation of a magnetic suspension, a ferrofluid, driven by circularly polarized magnetic field. Theory is tested by in vitro experiments and it is shown that, regardless of the character of the relaxation process, linearly and circularly polarized magnetic field excitations, having the same root-mean-square magnitude, are equivalent in terms of heating efficiency. 相似文献
19.
V. M. Korovin 《Technical Physics》2010,55(9):1275-1282
A thin layer of a Newtonian magnetic fluid wetting the faced-down surface of a horizontal magnetized plate in a vertical magnetic
field is considered. The lower boundary of the layer is the interface with a stationary gas. The effect of magnetic forces
on the development of the Rayleigh-Taylor instability is considered in the linear formulation of the long-wave approximation
of ferrohydrodynamic equations. 相似文献
20.
We investigate the application of the Migdal-Kadanoff bond-moving renormalization group (RG) approach to fractal lattices.
We find the following two results: first, for inhomogeneous interaction lattice models, bond moving involving inequivalent
bonds is unsuitable because it violates the condition <Δ>=0 (Δ is the perturbation potential resulting from moving the bonds); second, the condition <Δ>=0 does not uniquely determine the way to move bonds; different choices of bond moving yield different RG recursion relations
and corresponding fixed points, which makes the conclusions concerning the phase transition quite uncertain. 相似文献