镍锰铁氧体纳米线阵列的制备与表征

采用真空负压灌注技术, 结合溶胶-凝胶法在多孔氧化铝模板的纳米孔洞中成功制备了平均直径为80 nm左右的Ni_{1- x}Mn_xFe₂O₄(x=0, 0.25, 0.5, 0.75) 纳米线阵列. XRD结果显示所制备的纳米线阵列为立方尖晶石结构, SEM和TEM的结果表明纳米线是由大量不同晶体取向的亚微晶粒联接组成. 磁测量结果显示, 随着Mn掺杂浓度的增加, 饱和磁化强度先增加而后减小, 这种变化与离子在尖晶石结构中的替代、占位变化有关. 相比于块体材料的NiFe₂O₄, 由于非线性磁结构比例的增加, 导致了线体NiFe₂O₄的饱和磁化强度降低.     

Effect of zinc substitution on magnetic and electrical properties of nanocrystalline nickel ferrite synthesized by refluxing method

Nanocrystalline Nickel ferrite (NiFe₂O₄) and Zn substituted nickel ferrite (NiZnFe₂O₄) have been synthesized by the refluxing method. These ferrites were characterized by XRD, TEM, Mossbauer spectroscopy and VSM in order to study the effect of zinc substitution in nickel ferrite. XRD diffraction results confirm the spinel structure for the prepared nanocrystalline ferrites with an average crystallite size of 14-16 nm. Lattice parameter was found to increase with the substitution of Zn²⁺ ions from 8.40 Å to 8.42 Å. TEM images confirmed average particle size of about 20 nm and indicates nanocrystalline nature of the compounds. A shift in isomeric deviation with the doublet was observed due to the influence of Zn substitution in the nickel ferrite. The Zn content has a significant influence on the magnetic behavior and electrical conductivity of NiFe₂O₄. Saturation magnetization drastically increased whereas room temperature electrical conductivity decreased due to the addition of Zn content in NiFe₂O₄, indicating super magnetic material with lesser coercivity.     

Magnetic resonance study of Ce and Gd doped NiFe2O4 nanoparticles

Present work is a study of temperature dependent electron paramagnetic resonance spectra of Ce and Gd doped nickel ferrite nanoparticles. The samples, synthesised by chemical route were characterised by X-ray diffractometer, electron paramagnetic resonance spectroscopy (EPR) and vibrating sample magnetometer (VSM). The average crystallite size of pure nickel ferrite is ∼64 nm and for Gd and Ce doped samples it is ∼20 nm and ∼14 nm, respectively. The EPR spectra were recorded from 120 to 300 K. Doping with Gd and Ce reduces the line width and g-value in comparison to that of pure nickel ferrite. Ce doped samples have the lowest values of both these parameters at room temperature. This indicates that Ce doped samples show lowest loss and is suitable for high frequency devices. EPR spin numbers are reduced while the spin relaxation time is increased after doping with rare earth ions. Gd doped samples have higher values of relaxation time and lower spin numbers in comparison to that of Ce doped samples. VSM results show that the magnetisation and coercivity are reduced after doping with both Ce and Gd rare earth ions.     

Swift heavy ion irradiation effects on structural,optical properties and ac conductivity of polypyrrole nanofibers

Polypyrrole (PPy) nanofibers have been synthesized by interfacial polymerization method and irradiated with 160?MeV Ni¹²⁺ ions under vacuum with fluences in the range of 10¹⁰–10¹²?ions/cm². High-resolution transmission electron microscopy results show that upon swift heavy ion (SHI) irradiation the PPy nanofibers become denser. The crystallinity of PPy nanofibers increases upon SHI irradiation, while their d-spacing decreases. Upon SHI irradiation, the polaron absorption band gets red-shifted indicating reduction in the optical band gap energy of the irradiated PPy nanofibers. The indirect optical band gap energy is decreased as compared to corresponding direct optical band gap energy. The number of carbon atoms per conjugation length (N) and carbon atoms per cluster (M) of the SHI-irradiated PPy nanofibers increase with increasing the irradiation fluence. Fourier transform infrared spectra reveal the enhancement in intensity of some characteristic vibration bands upon SHI irradiation. The thermal stability of the PPy nanofibers is enhanced on SHI irradiation. The charge carriers in both pristine and irradiated PPy nanofibers follow the correlated barrier hopping mechanism. Scaling of ac conductivity reveals that the conduction mechanism is independent of the SHI irradiation fluence.     

Effect of Mg substitution on the magnetic properties of NiCuZn ferrite nanoparticles prepared through a novel method using egg white

Nanocrystalline Mg-substituted NiCuZn ferrites were successfully synthesized, for the first time, by using metal nitrates and freshly extracted egg white. The thermal decomposition process of the nitrate-egg white precursors was investigated by thermogravimetric (TG) technique. X-ray diffraction (XRD) revealed that, single-phase cubic ferrites with average particle size of 23.9-35.1 nm were directly formed after ignition at 500 °C. No noticeable variation of lattice parameters with increasing magnesium content was observed, while X-ray densities were found to decrease. This can be explained on the basis of ionic radii and atomic masses of the substituted cation. Transmission electron microscope (TEM) shows that, particles are permanently magnetized and get agglomerated. The saturation magnetization (M_s) and coercivity (H_c) as a function of Mg content were investigated using vibrating sample magnetometer (VSM). It has been found that the M_s increases firstly up to x=0.2 and then decreases, while H_c continuously decreases. Magnetic susceptibility measurements give results which agree well with those obtained by VSM. The obvious decrease in the Curie temperature (T_C) with increasing Mg indicates that the ferrimagnetic grains are widely separated and enclosed by non-magnetic magnesium ions.     

Swift heavy ion irradiation-induced modifications of tris-(8-hydroxyquinoline)aluminum thin films

Tris-(8-hydroxyquinoline)aluminum (Alq₃), one of the most widely used light emitting and electron transport materials in organic luminescent devices, has been synthesized. Alq₃ thin films have been deposited by a thermal evaporation process on glass substrates. The effect of swift heavy ion (SHI) irradiation using 40 MeV Li³⁺ on the Alq₃ thin films has been studied by UV-visible, infrared, photoluminescence (PL) and time-resolved photoluminescence (TRPL) spectroscopy. From TRPL studies, it is found that the PL of Alq₃ thin films arises from two species corresponding to its two geometrical isomers, namely facial and meridional having two different life times. It is also confirmed that the PL and lifetimes of excitons decrease with the increase of ion fluences of SHI of 40 MeV Li³⁺, indicating a transfer of exciton energy to unstable cationic Alq₃ species generated by SHI irradiation.     

Mössbauer and magnetic studies in nickel ferrite nanoparticles: Effect of size distribution

The magnetic properties of nickel ferrite nanoparticles in the form of powders, prepared by the sol-gel process and subjected to different annealing temperatures, were investigated using both static and dynamic measurements namely hysteresis, zero field cooled-field cooled magnetization (ZFC-FC) measurements and Mössbauer spectroscopy. The Transmission Electron Microscopy (TEM) studies reveal particle sizes for the as-prepared particles which increases upto 52 nm with annealing. A bimodal distribution, upto an annealing temperature of was observed. ZFC-FC measurements for the as-prepared samples reveal twin peaks, indicative of the bimodal size distribution. ZFC-FC measurements performed for fields varying from 100 Oe to 3 kOe show a superparamagnetic phase with blocking temperatures between 320 and . Numerical simulations for the ZFC-FC studies indicate that the signature of the bimodal size distribution can be seen only at very low fields. The variation of coercivity with particle size, as determined from the hysteresis measurements, shows a transition from a single domain to a multi domain state for particle sizes larger than 35 nm. Mössbauer measurements performed at room temperature for the as-prepared sample shows a six finger pattern for the samples with higher particle size and a doublet pattern for the samples with smaller particle size, which is indicative of their superparamagnetic nature.     

Investigation of magnetic properties of Al substituted nickel ferrite nanopowders, synthesized by the sol-gel method

NiFe_2−xAl_xO₄ nanopowders, where x is from 0 to 1.5 with a step of 0.5, have been synthesized by the sol-gel method and the effect of non-magnetic aluminum content on their structural and magnetic properties were investigated. The X-ray diffraction (XRD) patterns revealed that the synthesized nanopowders are single phase with a spinel structure. Mean crystallite sizes of the samples were calculated by Scherrer's formula and were in the range 20-31 nm. The morphology of the nanopowders was investigated by TEM and the mean particle sizes of the samples were in the range 55-80 nm. Magnetic hysteresis loops were recorded at room temperature in a maximum applied field of 3000 Oe. The results show that by increasing the aluminum content, the magnetizations of the nanopowders are decreased. This reduction is caused by non-magnetic Al³⁺ ions, which by their substitutions the super exchange interactions between different sites will be reduced. It is also seen that the magnetizations of the nanopowders are lower than those related to their bulk counterparts. This reduction was found to be as a consequence of surface spin disorder. M-T curves of the samples were obtained using a Faraday balance and by which the Curie temperatures of the powders were determined. The results that are obtained show that the Curie temperatures of the nanopowders are higher than those of their bulk counterparts.     

Swift heavy ion induced surface modifications in nano-crystalline Li-Mg ferrite thin films

The swift heavy ion (190 MeV Au¹⁴⁺) induced modifications in surface morphologies of the nanocrystals of ferrite thin films have been extensively studied through the images of atomic force microscopy (AFM). In most of the irradiated films significant features like, the ditch and dike structures, have been observed through out the surface. We try to explain the observed changes on the basis of thermal spike model followed by momentum transfer induced lateral mass transport. In addition to these changes some new and interesting features have been noticed after irradiation in 8F and 9F ferrite thin films. These new features are attributed to sputtering phenomenon due to the presence of defects like latent tracks.     

Swift heavy ion induced modifications in cobalt doped ZnO thin films: Structural and optical studies

Modifications in the structural and optical properties of 100 MeV Ni⁷⁺ ions irradiated cobalt doped ZnO thin films (Zn_1−xCo_xO, x = 0.05) prepared by sol-gel route were studied. The films irradiated with a fluence of 1 × 10¹³ ions/cm² were single phase and show improved crystalline structure with preferred C-axis orientation as revealed from XRD analysis. Effects of irradiation on bond structure of thin films were studied by FTIR spectroscopy. The spectrum shows no change in bonding structure of Zn-O after irradiation. Improved quality of films is further supported by FTIR studies. Optical properties of the pristine and irradiated samples have been determined by using UV-vis spectroscopic technique. Optical absorption spectra show an appreciable red shift in the band gap of irradiated Zn_1−xCo_xO thin film due to sp-d interaction between Co²⁺ ions and ZnO band electrons. Transmission spectra show absorption band edges at 1.8 eV, 2.05 eV and 2.18 eV corresponding to d-d transition of Co²⁺ ions in tetrahedral field of ZnO. The AFM study shows a slight increase in grain size and surface roughness of the thin films after irradiation.     

Polymer-templated mesoporous carbons synthesized in the presence of nickel nanoparticles, nickel oxide nanoparticles, and nickel nitrate

Mesoporous carbon composites, containing nickel and nickel oxide nanoparticles, were obtained by soft-templating method. Samples were synthesized under acidic conditions using resorcinol and formaldehyde as carbon precursors, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock co-polymer Lutrol F127 as a soft template and nickel and nickel oxide nanoparticles, and nickel nitrate as metal precursors. In addition, a one set of samples was obtained by impregnation of mesoporous carbons with a nickel nitrate solution followed by further annealing at 400 °C. Wide angle X-ray powder diffraction along with thermogravimetric analysis proved the presence of nickel nanoparticles in the final composites obtained using nickel and nickel oxide nanoparticles, and Ni(NO₃)₂ solution. Whereas, the impregnation of carbons with a nickel nitrate solution followed by annealing at 400 °C resulted in needle-like nickel oxide nanoparticles present inside the composites’ pores. Low-temperature (−196 °C) nitrogen physisorption, X-ray powder diffraction, and thermogravimetric analysis confirmed good adsorption and structural properties of the synthesized nickel-carbon composites, in particular, the samples possessed high surface areas (>600 m²/g), large total pore volumes (>0.50 cm³/g), and maxima of pore size distribution functions at circa 7 nm. It was found that the composites were partially graphitized during carbonization process at 850 °C. The samples are stable in an air environment below temperature of 500 °C. All these features make the synthesized nickel-carbon composites attractive materials for adsorption, catalysis, energy storage, and environmental applications.     

Defects induced magnetic transition in Co doped ZnS thin films: Effects of swift heavy ion irradiations

The effect of swift heavy ions (SHI) on magnetic ordering in ZnS thin films with Co ions substituted on Zn sites is investigated. The materials have been synthesized by pulsed laser deposition on substrates held at 600 °C for obtaining films with wurtzite crystal structure and it showed ferromagnetic ordering up to room temperature with a paramagnetic component. 120 MeV Ag ions have been used at different fluences of 1×10¹¹ ions/cm² and 1×10¹² ions/cm² for SHI induced modifications. The long range correlation between paramagnetic spins on Co ions was destroyed by irradiation and the material became purely paramagnetic. The effect is ascribed to the formation of cylindrical ion tracks due to the thermal spikes resulting from electron–phonon coupling.     

Investigate the ultrasound energy assisted adsorption mechanism of nickel(II) ions onto modified magnetic cobalt ferrite nanoparticles: Multivariate optimization

In present study, magnetic cobalt ferrite nanoparticles modified with (E)-N-(2-nitrobenzylidene)-2-(2-(2-nitrophenyl)imidazolidine-1-yl) ethaneamine (CoFe₂O₄-NPs-NBNPIEA) was synthesized and applied as novel adsorbent for ultrasound energy assisted adsorption of nickel(II) ions (Ni²⁺) from aqueous solution. The prepared adsorbent characterized by Fourier transforms infrared spectroscopy (FT-IR), transmission electron microscope (TEM), vibrating sample magnetometer (VSM) and X-ray diffraction (XRD). The dependency of adsorption percentage to variables such as pH, initial Ni²⁺ ions concentration, adsorbent mass and ultrasound time were studied with response surface methodology (RSM) by considering the desirable functions. The quadratic model between the dependent and independent variables was built. The proposed method showed good agreement between the experimental data and predictive value, and it has been successfully employed to adsorption of Ni²⁺ ions from aqueous solution. Subsequently, the experimental equilibrium data at different concentration of Ni²⁺ ions and 10 mg amount of adsorbent mass was fitted to conventional isotherm models like Langmuir, Freundlich, Tempkin, Dubinin-Radushkevich and it was revealed that the Langmuir is best model for explanation of behavior of experimental data. In addition, conventional kinetic models such as pseudo-first and second-order, Elovich and intraparticle diffusion were applied and it was seen that pseudo-second-order equation is suitable to fit the experimental data.     

Reduced conductivity and enhancement of Debye orientational polarization in lanthanum doped cobalt ferrite nanoparticles

In this work we have investigated the conductivity and dielectric properties of CoLa_xFe_2−xO₄ (x=0.0, 0.03, 0.05, and 0.07) nanoparticles synthesized by chemical co-precipitation route. X-ray diffraction analysis confirms the inverse spinal structure of nanoparticles with slight increase in the lattice constant as La concentration increases. Transmission electron microscopy shows spherical nanoparticles with sizes of ∼20 nm. Impedance spectroscopy of the samples was performed in the frequency range 20 Hz-2 MHz at room temperature. The resistance of the grains and grain boundaries was found to increase with lanthanum concentration while the AC conductivity of the samples was observed to decrease with increasing La concentration. Dipolar orientational polarization was found to play an important role in determining dielectric properties of the samples.     

Strontium ferrite nanoparticles synthesized in presence of polyvinylalcohol: Phase composition,microstructural and magnetic properties

Systematic study was devoted to the synthesis of hexagonal strontium ferrite nanoparticles employing polyvinylalcohol as stabilizing agent. Preliminary experiments allowed to select an optimal sol having molar ratio Sr²⁺/Fe³⁺=12${\mathrm{Sr}}^{2+}/{\mathrm{Fe}}^{3+}=12$, weight ratio PVA/[Sr²⁺+Fe³⁺]=1.4$\mathrm{PVA}/[{\mathrm{Sr}}^{2+}+{\mathrm{Fe}}^{3+}]=1.4$ and pH=2.1$\mathrm{pH}=2.1$. The obtained sol were transformed to gels by an evaporation of water at 100 °C and drying at 112 °C under vacuum. The subsequent calcination was carried out for 3 h at 400 °C, achieved by heating rate of 17 K/min. The obtained precursor was used for a detail study of influence of annealing conditions (temperature range 600–700 °C, annealing time 10–190 min) on the resulting properties. Semiquantitative X-ray phase analysis approved a gradual increase of the M-phase content and a gradual growth of M-phase crystallites with temperature and time. Magnetic measurements showed a distinct influence of the phase composition, namely ratio of the contents of M-phase and maghemite on the shape of the magnetic loops, while the crystallite sizes have only a slight effect.     

Temperature dependence of magnetic anisotropy constant in cobalt ferrite nanoparticles

The temperature dependence of the effective magnetic anisotropy constant K(T) of CoFe₂O₄ nanoparticles is obtained based on the SQUID magnetometry measurements and Mössbauer spectroscopy. The variation of the blocking temperature T_B as a function of particle radius r is first determined by associating the particle size distribution and the anisotropy energy barrier distribution deduced from the hysteresis curve and the magnetization decay curve, respectively. Finally, the magnetic anisotropy constant at each temperature is calculated from the relation between r and T_B. The resultant effective magnetic anisotropy constant K(T) decreases markedly with increasing temperature from 1.1×10⁷ J/m³ at 5 K to 0.6×10⁵ J/m³ at 280 K. The attempt time τ₀ is also determined to be 6.1×10⁻¹² s which together with the K(T) best explains the temperature dependence of superparamagnetic fraction in Mössbauer spectra.     

Cobalt ferrite nanoparticles: The control of the particle size and surface state and their effects on magnetic properties

In order to improve the efficacy of magnetic fluid hyperthermia (MFH) mediators, we synthesised cobalt ferrite nanoparticles with different sizes (between 5 and 7 nm) via successive polyol synthesis. The static and dynamic magnetic properties of the prepared particles, dispersed in a solid matrix, were investigated in order to evaluate the possibility of applying cobalt ferrite as magnetic susceptors in MFH. The effect on magnetic properties coming from the surface anchoring of the model molecule cetyl phosphate, was also investigated.     

Defect concentration profiles near the surface in nickel irradiated with 2 MeV electrons

Abstract

In the next nearest surface region the vacancy concentration is constant and independent of the irradiation temperature between 750 and 300°C and decreases with increasing electron flux. The conentrations of interstitials and of vacancies in the sink-free bulk of the material are equal and depend on the irradiation temperature, and are almost independent of the irradiation flux. The activation migration energies of vacancies and of interstitials decrease with increasing irradiation flux.It is further shown that the dynamic steady state defect concentrations resulting from the rate equations are artificial concentrations, which will not be achieved in finite times.     

Chemical synthesis of spinel nickel ferrite (NiFe2O4) nano-sheets

The present investigation is related to the deposition of single-phase nano-sheets spinel nickel ferrite (NiFe₂O₄) thin films onto glass substrates using a chemical method. Nano-sheets nickel ferrite films were deposited from an alkaline bath containing Ni²⁺ and Fe²⁺ ions. The films were characterized for their structural, surface morphological and electrical properties by means of X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and two-point probe electrical resistivity techniques. The X-ray diffraction pattern showed that NiFe₂O₄ nano-sheets are oriented along (3 1 1) plane. The FT-IR spectra of NiFe₂O₄ films showed strong absorption peaks around 600 and 400 cm⁻¹ which are typical for cubic spinel crystal structure. Microstructural study of NiFe₂O₄ film revealed nano-sheet like morphology with average sheet thickness of 30 nm. The room temperature electrical resistivity of the NiFe₂O₄ nano-sheets was 10⁷ Ω cm.     

γ-α相变中不同晶界特征下铁素体生长形貌的相场模拟

利用多相场模型模拟了奥氏体(γ)-铁素体(α)相变过程中不同晶界特征下铁素体晶粒的形貌与生长动力学.模型中通过能量梯度系数和耦合项系数的协同变化定量表达晶界能与晶界迁移率的各向异性,同时固定相场界面宽度来保证计算精度.模拟结果显示:随着原奥氏体晶界能与铁素体-奥氏体晶界能比值σ_(γ,γ)/σ_(α,γ)的增加,三叉相界面处的平衡角β减小,铁素体晶粒沿原奥氏体晶界与垂直于奥氏体晶界方向的生长速率差变大.铁素体与奥氏体晶粒间的晶粒取向越接近,铁素体生长越缓慢.模拟结果可描述铁素体晶粒生长形貌的多样性,与实验结果符合.