Influence of copper cations on the magnetic properties of NiCuZn ferrite nanoparticles

Ni_0.6−xCu_xZn_0.4Fe₂O₄ (x=0-0.5) ferrite nanoparticles were prepared, employing a reverse micelle process. X-ray diffraction and transmission electron microscopy evaluations demonstrated that single phase spinel ferrites with narrow size distribution were obtained. Vibrating sample magnetometer was employed to probe the magnetic properties of the samples. It was found that with an increase in copper content, the saturation magnetization decreases. Magnetic dynamics of the samples was studied by measuring a.c. magnetic susceptibility versus temperature at different frequencies. The phenomenological Néel-Brown and Vogel-Fulcher models were employed to distinguish between the interacting or non-interacting systems. The system exhibits that there is strong interaction among fine particles.     

Influence of impurities on the low-temperature deformation of nanocrystalline copper

The influence of ZrO₂ particles on the low-temperature deformation of nanocrystalline copper produced by strong plastic deformation is investigated using equichannel angular pressing. A comparison is made between the deformation characteristics in tension and compression in the temperature range 4.2–400 K, measured for copper and the composite Cu:0.3 vol. % ZrO₂. It is shown that within 4.2–200 K the yield point σ _sm of the composite is higher than that for copper, attaining 680 MPa at 4.2 K, then the yield points are close in value up to room temperature, and diverge again as the temperature is raised. Possible causes of the dissimilar influence of an impurity on the strength and plasticity characteristics of nanocrystalline copper in various temperature intervals are discussed. Fiz. Tverd. Tela (St. Petersburg) 40, 1639–1641 (September 1998)     

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.     

The electrical property dependence of disordered copper oxide on oxygen content

We have deposited disordered copper oxide films on glass substrates, with varying oxygen to copper ratios, by the reactive sputtering method. The variation in the ratio is enough to take the system from having disordered metallic like conduction at low oxygen content to hopping like behaviour at higher oxygen content. The hopping like behaviour is described by an unusual band structure, where Mott-variable range hopping is seen at lower temperatures and electron-electron variable range hopping at higher temperatures in some samples. The metallic region shows the expected effects of quantum corrections to the conductivity, with the often seen influence of spin-orbit scattering in copper. The transition between the hopping and metallic state is of the percolation type, where the conduction path between Cu islands is broken as the oxygen content increases.     

The structural and optical property dependence of disordered copper oxide on oxygen content

This study has investigated the optical and structural properties of reactively sputtered copper oxide. The investigated Cu to O ratio (oxygen content) spans the metal-insulator transition. Initially, the number of copper crystallites reduces and Cu₂O crystallite numbers increase with increasing oxygen content, this then turns to a crystallite evolution of Cu₂O to CuO as the oxygen content is increased above the nominal value for Cu₂O, with no copper crystallites remaining. Along with the change in the structure, the system smoothly evolves from optically being metallic in nature to being band gap like, with increasing oxygen content.     

Radio-frequency-heating capability of silica-coated manganese ferrite nanoparticles

Mn Fe2O4nanoparticles(NPs) with various sizes and tight size-distribution were synthesized by a chemical solutionphase method.The as-synthesized NPs were coated with a silica shell of 4 nm–5 nm in thickness,enabling the watersolubility and biocompatibility of the NPs.The Mn Fe2O4 NPs with a size of less than 18 nm exhibit superparamagnetic behavior with high saturated magnetization.The capacity of the heat production was enhanced by increasing particle sizes and radio frequency(RF) field strengths.Mn Fe2O4/Si O2 NPs with 18-nm magnetic cores showed the highest heatgeneration ability under an RF field.These Mn Fe2O4/Si O2 NPs have great potentiality to cancer treatments,controlled drug releases,and remote controls of single cell functions.     

Insight into magnetic properties in zinc ferrite thin films by tuning oxygen content

In this investigation ZnFe₂O₄ thin films were fabricated by RF magnetron sputtering and the magnetic behavior was examined under the influence of the growth conditions in three types of atmospheres, using near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and vibrating sample magnetometry (VSM). XPS revealed that films under an Ar/O₂ ratio 1:2 and 2:1 have Fe/Zn atomic ratios similar to the Fe/Zn stoichiometric composition; while the films deposited in pure Ar atmosphere, showed a formation of Fe ions (Fe⁰) reduced by Ar ion sputtering. VSM revealed an enhancing of the saturation magnetization for the ZFO in thin films unlike the samples in bulk, suggesting that Fe ions migrate to A sites and the interaction J_AB dominates the magnetic properties instead of J_BB interaction.     

Influence of dissolved oxygen content on multibubble sonoluminescence with ambient-pressure reduction

The efficiency of chemical reactions in the presence of ultrasound at reduced pressures has been monitored using the influence of dissolved oxygen (DO) content on a luminol solution undergoing multibubble sonoluminescence. From these measurements under the condition of constant ultrasonic frequency and constant amplitude of sound pressure, it is shown that the intensity of sonoluminescence is higher at subatmospheric ambient pressure than at atmospheric pressure under the same degree of saturation. Also, it is found that there is an appropriate content of DO to produce the highest intensity of the luminescence and its value varies with ambient pressure.     

Influence of magnetic anisotropy constant and particle domain magnetization on magneto-dielectric response of substituted manganese ferrite particles dispersed in kerosene

This paper presents a dielectric and magneto-dielectric study of magnetic fluids made of three different, partially substituted, manganese ferrite particles dispersed in kerosene. Measurements were performed using a wholly automated spectrometer in the frequency range 1 mHz–10 MHz and a temperature range from −200°C up to 100°C. We can distinguish the two phases (solid and liquid) in pure kerosene and three phases for all the magnetic fluid samples. We observed the effect of anisotropy constant and domain magnetization of the particles on magneto-dielectric measurements. We also observed the temperature sensitivity of these fluids.     

Size and compositionally controlled manganese ferrite nanoparticles with enhanced magnetization

The effects of solvents on the anatase crystallite size prepared by sol–gel microwave-assisted solvothermal method were investigated in this study. Eight different alcohol solvents classified into two groups, i.e. primary and secondary/ternary alcohols, were used as reaction media and the effects of solvent properties, such as dielectric constant, boiling point, and internal pressure during the solvothermal process, on the crystallite size and shape were analyzed. According to the experimental results, selecting the solvent type allowed not only the alteration of the crystallite size but also the crystallite shape without the need of any additives. The boiling point of solvent was determined as the major factor influencing the crystallite size. Among the solvents with similar boiling points, the solvent with a higher carbon number produced the smaller crystallite size because of steric hindrance effect. In addition, the carboxyl groups dissociated from the alcohol solvent can play a role as a structural capping agent to retard the anatase crystal growth along the [001] direction and led to a rectangular crystallite shape with preferred development in {001} facets. On the other hand, the alcoholysis reaction was found easily occurred between the primary alcohol and isopropoxide that effectively limited the hydrolysis and condensation processes but also suppressed the structural capping effect. Therefore, the anatase crystals prepared in the primary alcohols became exceptionally small and showed spherical shape. Finally, the anatase crystals prepared using isopropanol demonstrated the highest photocatalytic activity due to its evident preferred crystallization in the {001} facets.     

The perminvar effect and magnetic after-effect in magnesium manganese ferrite

An unstable perminvar effect was found in magnesium manganese ferrite at a temperature of –195°C and its connection with the magnetic after-effect was investigated. The analysis carried out on the basis of Néel's theory showed that both effects are a result of the same diffusion process. The experimental results also show that 180° Bloch walls are displaced when the sample is magnetized.

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Studies on the activation energy from the ac conductivity measurements of rubber ferrite composites containing manganese zinc ferrite

Manganese zinc ferrites (MZF) have resistivities between 0.01 and 10 Ω m. Making composite materials of ferrites with either natural rubber or plastics will modify the electrical properties of ferrites. The moldability and flexibility of these composites find wide use in industrial and other scientific applications. Mixed ferrites belonging to the series Mn_(1−x)Zn_xFe₂O₄ were synthesized for different ‘x’ values in steps of 0.2, and incorporated in natural rubber matrix (RFC). From the dielectric measurements of the ceramic manganese zinc ferrite and rubber ferrite composites, ac conductivity and activation energy were evaluated. A program was developed with the aid of the LabVIEW package to automate the measurements. The ac conductivity of RFC was then correlated with that of the magnetic filler and matrix by a mixture equation which helps to tailor properties of these composites.     

The infrared absorption spectrum and the inversion degree of manganese ferrite

Infrared spectra of MnFe₂O₄ with inversion degrees of 0.05 and 0.2 are reported. It can be concluded that the absorption observed at 335 cm^?1 has to be the third fundamental IR active mode.     

Synthesis and characterization of manganese ferrite nanoparticles by thermal treatment method

Cubic structured manganese ferrite nanoparticles were synthesized by a thermal treatment method followed by calcination at various temperatures from 723 to 873 K. In this investigation, we used polyvinyl pyrrolidon (PVP) as a capping agent to control the agglomeration of the nanoparticles. The characterization studies were conducted by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The average particle sizes of manganese ferrite nanoparticles were determined by TEM, which increased with the calcination temperature from 12 to 22 nm and they had good agreement with XRD results. Fourier transform infrared spectroscopy confirmed the presence of metal oxide bands at all temperatures and the absence of organic bands at 873 K. Magnetic properties were demonstrated by a vibrating sample magnetometer, which showed a super-paramagnetic behavior for all samples and also saturation magnetization (M_s) increases from 3.06 to 15.78 emu/g by increasing the calcination temperature. The magnetic properties were also confirmed by the use of electron paramagnetic resonance spectroscopy, which revealed the existence of unpaired electrons and also measured peak-to-peak line width, resonant magnetic field and the g-factor.     

Mössbauer spectroscopic characterization of manganese and cobalt ferrite ferrofluids

Aqueous ferrofluids based on Mn and Co ferrites have been synthesized by a novel method. Mössbauer spectra of dried samples (average particle diameter ≈ 10 nm) were measured in the 77–340 K temperature range. CoFe₂O₄ spectra show no superparamagnetic (SP) relaxation, in accordance with the high magnetic anisotropy of this compound. MnFe₂O₄ spectra exhibit SP relaxation, from which an effectiveK=(8±3)×10⁴ J/m³ is estimated. This value represents a 20× enhancement over intrinsic magnetocrystalline anisotropy.