Papers by Keyword: Superparamagnetism

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Authors: A. Lukawska, Z. Jagoo, Gregory Kozlowski, Z. Turgut, H. Kosai, A. Sheets, T. Bixel, A. Wheatley, P. Abdulkin, B. Knappett, T. Houlding, V. Degirmenci
Abstract: AC magnetic heating of superparamagnetic Co and Fe nanoparticles for application in hyperthermia was measured to find a size of nanoparticles that would result in an optimal heating for given amplitude and frequency of ac externally applied magnetic field. To measure it, a custom-made power supply connected to a 20-turn insulated copper coil in the shape of a spiral solenoid cooled with water was used. A fiber-optic temperature sensor has been used to measure the temperature with an accuracy of 0.0001 K. The magnetic field with magnitude of 20.6 μT and a frequency of oscillation equal to 348 kHz was generated inside the coil to heat magnetic nanoparticles. The maximum specific power loss or the highest heating rate for Co magnetic nanoparticles was achieved for nanoparticles of 8.2 nm in diameter. The maximum heating rate for coated Fe was found for nanoparticles with diameter of 18.61 nm.
Authors: Laszlo F. Kiss, J. Balogh, L. Bujdosó, D. Kaptás, T. Kemény, T. Pusztai, I. Vincze
Authors: Tatiana S. Gendler, Alla A. Novakova, V.N. Prudnikov, G.P. Aleksandrova, L.A. Grishchenko
Abstract: The comparative study of Fe2O3 4-10nm nanoparticles incorporated in arabinogalactan and polyvinyl alcohol matrixes was performed by means of magnetic measurements in wide 5-900K temperature range, Mossbauer spectroscopy and transmission electron microscopy. The processes of nanoparticles different self-organization inside various polymer matrixes were revealed. These processes lead to unusual magnetic behavior of initially superparamagnetic nanoparticles owing to interparticle interactions.
Authors: V.V. Ustinov, L.N. Romashev, M.A. Milyaev, T.P. Krinitsina, A.M. Burkhanov
Abstract: The magnetic and magnetoresistive properties of nanostructured Fe/Cr multilayers with ultra-thin Fe layers (the nominal Fe thickness tFe is down to 0.3 Å) have been investigated at low temperatures (down to 2 K) in magnetic fields up to 90 kOe. Nanostructures were MBE grown in ultrahigh vacuum on single crystal MgO substrates. It is shown that Fe layers in nanostructures with tFe < 2 Å are not continuous but consist of separate ferromagnetic clusters. Such cluster-layered nanostructures exhibit superparamagnetic properties and the Kondo-like behavior of resistivity.
Authors: Vladimir S. Pechnikov
Abstract: In article results of research of the saturation magnetic moment temperature dependence of ferromagnetic amorphous tapes on an iron and cobalt basis, and also one not ferromagnetic amorphous tape are described. It is shown that in an initial condition not all atoms of magnetic elements are in a ferromagnetic phase. Temperature dependence of the saturation moment of a ferromagnetic phase of amorphous tapes is well described by Brillouin's function. Possibility of quantitative definition of part of the magnetic atoms forming not ferromagnetic phase of a tape is proved. It is shown that the tape on the iron basis, containing about 20% of chrome, not ferromagnetic in an initial condition, consists of the superparamagnetic nanoparticles including about 10 atoms of iron.
Authors: Yury Dikansky, Anna Ispiryan, Stanislav Kunikin, Alexandr Radionov
Abstract: Temperature dependence of the low-frequency complex magnetic susceptibility of magnetic colloid with paraffin as a dispersion medium has been studied. When interpreting the obtained results, the specific features of the magnetic moment relaxation of single-domain particles and the possibility of changing of relaxation mechanism from Neel to Brownian have been considered.
Authors: Jérôme Leveneur, John Kennedy, Grant V. M. Williams, Fang Fang, James B. Metson, Andreas Markwitz
Abstract: We have fabricated surface magnetic iron nanoclusters using low energy Fe+ implantation and electron beam annealing. We find that changing the fluence has a significant effect on the nanocluster growth, structural and magnetic properties. Low fluences lead to small nanoclusters and superparamagnetism, while high fluences result in larger chain-like nanoclusters that have high remnant magnetizations and a significantly reduced saturation field. Our results show that the nanostructure and the magnetic properties can be tuned by varying the Fe+ fluence, which means that a reliable method can be used to make surface nanoclusters for a variety of applications (e.g. large magnetoresistance sensors with no hysteresis).
Authors: M. Raghasudha, D. Ravinder, P. Veerasomaiah
Abstract: The work deals with the study of electrical and magnetic properties of Magnesium-Chromium and Cobalt-Chromium nanoFerrites for their potential applications synthesized by Citrate-Gel auto-combustion method. Structural Characterization of prepared nanoferrites was performed using XRD, SEM, EDS and TEM. XRD patterns confirmed the formation of homogeneous single phased cubic spinel belonging to the space group Fd3m (in agreement with ICSD Ref. data). It is found that crystallite size of Mg-Cr ferrites was in the range of 7-23nm and that of Co-Cr nanoferrites in the range of 6-12 nm. Structural morphology of both the ferrites was studied by SEM (Scanning Electron Microscopy) and TEM (Transmission Electron Microscopy). Elemental compositional analysis was carried out by EDS.Electrical properties such as D.C. resistivity of prepared Mg-Cr and Co-Cr nanoferrites were studied by two probe method. The dielectric measurements as a function of frequency at room temperature were performed in the frequency range of 20Hz to 2MHz using LCR meter. Various dielectric parameters like dielectric constant (ε′), dielectric loss (ε′′) and dielectric loss tangent (tan δ) were measured as a function of frequency. The magnetization measurements of the prepared nanoferrite samples were carried out at room temperature in the applied field of ±15KOe using Vibrating Sample Magnetometer (VSM). From the obtained M-H loops, various magnetic parameters such as Saturation Magnetization (Ms), Coercivity (Hc) and Remanence Magnetization (Mr) were measured. Magnetization as a function of field (±10T) at 5K, 25K, 300K temperatures was measured using VSM. Super-paramagnetic nature of some specified samples in Mg-Cr nanoferrites system was investigated from the temperature dependence of both the field cooled (FC) and the zero-field cooled (ZFC) magnetization measurements under a field of 100 Oe in the temperature range 5K to 350K.From the results of D.C. resistivity measurements it is observed that the resistivity decreases with increase in temperature for both Mg-Cr and Co-Cr nanoferrites suggesting the semiconducting behavior of the samples. Dielectric measurements suggest that the conduction in the ferrite systems may be due to the polaron hopping mechanism. The low loss tangent values at high frequency show the potential applications of these materials in high frequency microwave devices. Mg-Cr nanoferrites were synthesized yielding narrow hysteresis loops which are the characteristic of very soft magnetic materials that are desirable for their utility in Transformers, Inductor cores, Microwave devices and Magnetic shielding. Hysteresis loops of Co-Cr nanoferrites show the medium hard magnetic behavior of the materials. MgFe2O4 shows superparamagnetic behavior above room temperature and MgCr0.9Fe1.1O4 shows superparamagnetic behavior with the blocking temperature 94.5K. Hence these nanoferrites find applications in targeted drug delivery and in Magnetic Resonance Imaging (MRI) in biomedical field. The observed results can be explained in detail on the basis of composition and crystallite size.Contents of Paper
Authors: Zhen Yu Wu, Hai Long Dong, Andrey L. Chuvilin, Ulf Wiedwald, Lu Yang Han, Carl E. Krill III
Abstract: The preparation of a novel ferrofluid out of one-dimensional magnetic structures is attempted by the reverse-micelle-based wet-chemical formation of FePt nanowires and nanorods. The latter were found to manifest lengths ranging from 25 to 250 nm, with an average diameter of only 1.5 to 2 nm. X-ray diffraction and high-resolution TEM revealed a polycrystalline microstructure, with individual grains having the disordered fcc structure in the as-prepared state; a thermally induced transition to the chemically ordered phase was observed around 550°C. The samples were determined to be superparamagnetic at room temperature, with the blocking temperature measured to be ~26 K.
Authors: Gerardo F. Goya, M.P. Morales
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