Magnetic and Distribution of Magnetic Moments in Amorphous Fe89.7P10.3 Alloy Nanowire Arrays

Binary amorphous Fe89.7P10.3 alloy nanowire arrays in been fabricated in an anodic aluminium oxide template diameter of about 40nm and length of about 3μm have by electrodeposition. Magnetic properties of the samples are investigated by mean of vibrating sample magnetometer, transmission Mossbauer spectroscopy and conversion electron Mossbauer spectroscopy at room temperature. It is found that the nanowire arrays have obvious perpendicular magnetic anisotropy, and are ferromagnetic at room temperature, with its Mossbauer spectra consisting of six broad lines. The average angles between the Fe and 28° at the end of the amorphous Fe89.7P10.3 alloy magnetic moment and the wire axis are about 14°inside nanowire arrays, respectively. The magnetic behaviour is decided by the shape anisotropy and the dipolar interaction between wires. In addition, the magnetic moments distribution is theoretically demonstrated by using the symmetric fanning mechanism of the spheres chain model.     

Electrical Properties of Nanostructured Magnetic Colloid and Influence of Magnetic Field

We investigate the electrical properties of the nanostructured magnetic colloid without and with magnetic field. The competition between the directional motion of the charged magnetic nanoparticles and other minor nonmagnetic impurities （also small amount of ions） under applied voltage and their random orientation due to thermal activation is implemented to elaborate the electrically conduction mechanism under zero magnetic field. Two equivalent electric circuits are employed for explaining the charging and discharging processes. The tunnelling conduction mechanism upon application of externally magnetic field may exist in the nanostructured magnetic colloid. The alternation of the two conduction mechanisms accounts for the current spikes when the magnetic field is switched on or off. This work presents the peculiar electrical phenomena of the magnetically colloidal system.     

Transition Metal Silicide Nanowires Growth and Electrical Characterization

We report the characterization of self-assembled epitaxially grown transition metal, Fe, Co, Ni, silicide nanowires （TM-NW） growth and electrical transport properties. NWs grown by reactive deposition epitaxy on various silicon surfaces show a dimension of 10nm by 5nm, and several micrometers in length. NW orientations strongly depend on substrate crystal orientation, and follow the substrate symmetry. By using conductive-AFM （c-AFM）, the electron transport properties of one single NW were measured, the resistivity of crystalline nickel silicide NW was estimated to be 2×10-2Ω＆#12539;cm.     

Fabrication and Characterization of SmCo5/Fe65Co35 and SmCo5/Fe Composite Spring Exchange Magnets

SmCo5/Fe65Co35 and SmCo5/Fe spring exchange magnets are fabricated by dc magnetron sputtering on MgO substrates and 100-nm-thick Si3N4 membranes, respectively. The base pressure of sputtering chamber is kept below 10^-7 Tort, and Ar pressure is 3 to 8mTorr. The samples are characterized by an x-ray diffractometer, a superconducting quantum interference magnetometer, and high resolution magnetic soft x-ray microscopy. We obtain the complete exchange coupling and single phase behaviour of composite magnets. The （BH）max value achieved is 28.8 MGOe.     

Enhanced Magnetoresistance of （La0.67Ca0.33MnO3） Composites Coated by Zn0.95Co0.05O

La0.7Ca0.3MnO3：xZn0.95Co0.05O （x=0.0,0.05, 0.1, 0.15mol） composites are prepared by a sol-gel process. X- ray diffraction and energy diffraction spectroscopy reveal that there is no evidence of a reaction between the La0.7 Ca0.3 MnO3 （LCMO） and Zn0.95Co0.05 O （ZCO）. Magnetization M, Curie temperature Tc and metal-insulator transition temperatures Tp are observed to decrease with increasing ZCO content. Compared with x = 0.0, a great enhancement in the magnetoresistance （MR） is observed at around Tc for x = 0.05, 0.10, 0.15. Based on the tunneling MR and percolation models, this great change of MR is well explained.     

Electroluminescence of Si Nanocrystal-Doped SiO2

We perform a comparative st udy on the electroluminescence （EL） and photoluminescence （PL） of Si nanocrystaldoped SiO2 （nc-Si：SiO2） and SiO2, and clarify whether the contribution from Si nanocrystals in the EL of nc-Si：SiO2 truly exists. The results unambiguously indicate the presence of EL of Si nanocrystals. The difference of peak positions between the EL and PL spectra are discussed. It is found that the normal method of passivation to enhance the PL of Si nanocrystals is not equally effective for the EL, hence new methods need to be explored to promote the EL of Si nanocrystals.[第一段]     

Microwave Magnetic Permeability of Fe3O4 Nanoparticles

Well-dispersed Fe3O4 nanoparticles are synthesized via an oxidization method with NANO2 as oxidant. The microwave magnetic properties of the composites are studied with different volume fractions of fe3O4 nanoparticles. It is found that a lower volume fraction corresponds to a higher magnetic resonance frequency. This could be ascribed to the enhancement of exchange interaction with a weakened dipolar interaction when the volume fraction decreases.     

Low-Temperature Magnetic Properties of Co Antidot Array

Cobalt antidot arrays with different thicknesses are fabricated by rf magnetron sputtering onto porous alumina substrates. Scanning electron microscopy and grazing incidence x-ray diffraction are employed to characterize the morphology and crystal structure of the antidot array, respectively. The temperature dependence of magnetic properties shows that in the temperature range 5K--300K, coercivity and squareness increase firstly, reach their maximum values, then decrease. The anomalous temperature dependences of coercivity and squareness are discussed by considering the pinning effect of the antidot and the magnetocrystalline anisotropy.     

Characterization and Magnetic Properties of Iron-Based Alloy Antidot Arrays

Fe29Cerl and Fe19Ni81 antidot arrays, with different dimensions, are prepared with the rf magnetron sputtering method onto the porous alumina substrate. The size and shape of antidot arrays are characterized by scanning electron microscopy. The glancing angle x-ray diffraction patterns of Fe29C071 and FelgNi81 antidot arrays indicate the bcc and fcc structures, respectively. The coercivities of both the alloys show abnormal thickness dependence, which are discussed qualitatively by considering the pinning and the thickness effect to the films.     

Magnetostriction and magnetoresistance in nanocontacts

Ni nanocontacts have been grown by electrodeposition using a self-terminating technique in a single electrolyte bath based on nickel sulfate, nickel chloride and boric acid. Resistance measurements performed on different samples presented two kinds of obviously different magnetoresistance effects. The analysis of the data sets showed that magnetostriction might play a key role in magnetoresistance of the electrodeposited Ni nanocontacts.     

Synthesis and magnetic properties of CoFe2O4 ferrite nanoparticles

CoFe₂O₄ ferrite nanoparticles were prepared by a modified chemical coprecipitation route. Structural and magnetic properties were systematically investigated. X-ray diffraction results showed that the sample was in single phase with the space group . The results of field-emission scanning electronic microscopy showed that the grains appeared spherical with diameters ranging from 20 to 30 nm. The composition determined by energy-dispersive spectroscopy was stoichiometry of CoFe₂O₄. The Curie temperature in the process of increasing temperature was slightly higher than that in the process of decreasing temperature. This can be understood by the fact that heating changed Co²⁺ ion redistribution in tetrahedral and in octahedral sites. The coercivity of the synthesized CoFe₂O₄ samples was lower than the theoretical values, which could be explained by the mono-domain structure and a transformation from ferrimagnetic to superparamagnetic state.     

Static susceptibility and heat capacity studies on V3O7·H2O7 nanobelts

V₃O₇·H₂O nanobelts were prepared by a hydrothermal method at 190 °C using V₂O₅·nH₂O gel and H₂C₂O₄·2H₂O as starting agents. The obtained nanobelts have diameters ranging from 40 to 70 nm with lengths up to several micrometers. Measurements of the static magnetic susceptibility and the specific heat show a discontinuous phase transition at around T=145 K, which separates two regions of paramagnetic behavior.     

Magnetic properties of xNi0.53Cu0.12Zn0.35Fe1.88O4+(1−x)BaTiO3 nanocomposites

The nanocrystalline Ni_0.53Cu_0.12Zn_0.35Fe_1.88O₄ and BaTiO₃ powders were prepared using Microwave-Hydrothermal (M-H) method at 160 °C/45 min. The as synthesized powders were characterized using the X-ray diffraction (XRD) and Transmission Electron Microscope (TEM). The size of the powders that were synthesized using M-H system was found to be ∼30 and ∼50 nm for ferrite phase and ferroelectric phases, respectively. The powders were densified using microwave sintering method at 900 °C/30 min. The ferrite and ferroelectric phases were observed from XRD and morphology of the composites was observed with the Scanning Electron Microscope (SEM).The magnetic hysteresis loops were recorded using the Vibrating Sample Magnetometer (VSM).The frequency dependence of real (μ′) and imaginary (μ″) parts of permeability was measured in the range of 1 MHz-1.8 GHz. The permeability decreases with an increase of BaTiO₃ content at 1 MHz. The transition temperature (T_C) of ferrite was found to be 245 °C. The T_C of composite materials decreases with an increase in BaTiO₃ content.     

Structural and magnetic properties of Co1−xZnxFe2O4 nanoparticles by co-precipitation method

Co_1−xZn_xFe₂O₄ nanoparticles were prepared by co-precipitation method with x varying from 0 to 1.0. The powder samples were characterized by X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and Fourier transform infrared spectroscopy (FTIR). The average crystallite sizes of the particles were determined from XRD. X-ray analysis showed that the samples were cubic spinel. The average crystallite size (D_aveXR) of the particles precipitated was found to vary from 6.92 to 12.02 nm decreasing with the increase in zinc substitution. The lattice constant (a_o) increased with the increase in zinc substitution. The specific saturation magnetization (M_S) of the particles was measured at room temperature. The magnetic parameters such as M_S, H_c, and M_r were found to decrease with the increase in zinc substitution. FTIR spectra of the Co_1−xZn_xFe₂O₄ with x varying from 0 to 1.0 in the range 400–4000 cm⁻¹ were reported. The spinel structure and the crystalline water adsorption of Co_1−xZn_xFe₂O₄ nanoparticles were studied by using FTIR.     

Permeability-frequency spectra of (Fe1−xcox)73.5Cu1Nb3Si13.5B9 nanocrystalline alloys under different magnetic fields

Under various amplitude of AC magnetic fields domain wall motion is the main mechanism in the magnetization process. This includes domain wall bulging and domain wall displacing. In this paper complex permeability-frequency spectra of (Fe_1−xCo_x)_73.5Cu₁Nb₃Si_13.5B₉ (x=0,0.5$x=0,0.5$) nanocrystalline alloys were measured as a function of the AC magnetic field, ranging from 0.001 to 0.04 Oe. Obvious changes have been found in complex permeability spectra for alloy x=0$x=0$ with the change of the amplitude of AC magnetic field, but variation of AC magnetic field has little effect on complex permeability spectra for alloy x=0.5$x=0.5$. This is attributed to the increased pinning field after substitution of Fe with Co in Fe_73.5Cu₁Nb₃Si_13.5B₉ nanaocrystalline alloy.     

Dielectric and Pyroelectric Properties of （Pb0.50Sr0.50）TiO3 Ceramics

Lead strontium titanate （Pb0.50Sr0.50）TiO3 （PST） ceramics are prepared by the traditional ceramic processing. The dielectric constants and dielectric loss have been investigated in a temperature range from 25℃ to 300℃. The maximum dielectric constants for unpoled and poled samples are 9924 and 9683, respectively. The temperatures of phase transition for unpoled and poled samples are observed at 153℃ and 157℃, respectively. The phasetransition temperatures for unpoled and poled samples are not equal, which results from the polarization state of the domains. The remnant polarization and the coercive electric field are 18 uC/cm^2 and 6 kV/cm, respectively, from polarization-electric field （P - E） hysteresis loop. The temperature dependence of pyroelectric coefficients of the PST ceramics is measured by a dynamic technique. The dielectric constant and loss Lan δ of the poled PST ceramics are 813 and 0.010, respectively. The pyroelectric coefficients and figure of merit are 294 uC/cm^2 K and 13.6 × 10^-6 pa^-0.5, respectively, at room temperature 25℃and frequency lOOHz.     

Magnetic properties of the novel nanocomposite (Zn0.15Ni0.85Fe2O4)0.15/(SiO2)0.85 at room temperature

The value of the effective magnetic anisotropy constant of the ferrimagnetic nanoparticles Zn_0.15Ni_0.85Fe₂O₄ embedded in a SiO₂ silica matrix, determined through ferromagnetic resonance (FMR), is much higher than the magnetocrystalline anisotropy constant. The higher value of the anisotropy constant is due to the existence of surface anisotropy. However, even if the magnetic anisotropy is high, the ferrimagnetic nanoparticles with a 15% concentration, which are isolated in a SiO₂ matrix, display a superparamagnetic (SPM) behavior at room temperature and at a frequency of the magnetization field equal to 50 Hz. The FMR spectrum of the novel nanocomposite (Zn_0.15Ni_0.85Fe₂O₄)_0.15/(SiO₂)_0.85, recorded at room temperature and a frequency of 9.060 GHz, is observed at a resonance field (B_0r) of 0.2285 T, which is substantially lower than the field corresponding to free electron resonance (ESR) (0.3236 T). Apart from the line corresponding to the resonance of the nanoparticle system, the spectrum also contains an additional weaker line, identified for a resonance field of ∼0.12 T, which is appreciably lower than B_0r. This line was attributed to magnetic ions complex that is in a disordered structure in the layer that has an average thickness of 1.4 nm, this layer being situated on the surface of the Zn_0.15Ni_0.85Fe₂O₄ nanoparticles that have a mean magnetic diameter of 8.9 nm.     

Solid state reaction synthesis of NiFe2O4 nanoparticles

Ni-ferrite (NiFe₂O₄) nanoparticles have been synthesized via a solid state reaction process. Ni and Fe bi-metallic nanoparticles in the form of Ni₃₃Fe₆₇ alloy nanopowder are first synthesized by simultaneous evaporation of the required amounts of pure Ni and Fe metals followed by rapid condensation of the evaporated metal flux into solid state by means of an inert gas, helium, using the process of inert gas condensation (IGC). In order to form the NiFe₂O₄ structure, as-synthesized samples (Ni₃₃Fe₆₇) are annealed for 12 h in ambient conditions at different annealing temperatures. Structural analyses show that NiFe₂O₄ starts to form at around 450 °C and gets progressively well defined with increasing annealing temperatures yielding particle with size ranging between 15 and 50 nm. Besides successfully forming NiFe₂O₄, NiO/Fe₃O₄ core/shell nanoparticles have also been synthesized by adjusting the annealing conditions. Three different structures, Ni₃₃Fe₆₇, NiO/Fe₃O₄, and NiFe₂O₄, obtained in this study are compared with respect to their structural and magnetic properties.     

Magnetic properties of nanocrystalline Co1−xZnxFe2O4 prepared by forced hydrolysis method

Nanocrystalline zinc-substituted cobalt ferrite powders, Co_1−xZn_xFe₂O₄ (x=0, 0.2, 0.4), were for the first time prepared by forced hydrolysis method. Magnetic and structural properties in these specimens were investigated. The average crystallite size is about 3.0 nm. When the zinc substitution increases from x=0 to x=0.4, at 4.2 K, the saturation magnetization increases from 72.1 to 99.7 emu/g and the coercive field decreases from 1.22 to 0.71 T. All samples are superparamagnetic at room temperature and ferrimagnetic at temperatures below the blocking temperature. The high value of the saturation magnetization and the very thin thickness of the disorder surface layer of all samples suggests that this forced hydrolysis method is suitable not only for preparing two metal element systems but also for three or more ones.     

Synthesis and magnetic properties of spinel CoFe2O4 nanowire arrays

Spinel CoFe₂O₄ nanowire arrays were synthesized in nanopores of anodic aluminum oxide (AAO) template using aqueous solution of cobalt and iron nitrates as precursor. The precursor was filled into the nanopores by vacuum impregnation. After heat treatment, it transformed to spinel CoFe₂O₄ nanowires. The structure, morphology and magnetic properties of the sample were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The results indicate that the nanowire arrays are compact. And the individual nanowires have a high aspect ratio, which are about 80 nm in diameter and 10 μm in length. The nanowires are polycrystalline spinel phase. Magnetic measurements indicate that the nanowire arrays are nearly magnetic isotropic. The reason is briefly discussed. Moreover, the temperature dependence of the coercive force of the nanowire arrays was studied.