Magnetic properties of NiCuZn ferrite nanoparticles synthesized using egg-white

A new process to prepare single-phase nano-sized ferrites, Ni_0.8−xCu_0.2Zn_xFe₂O₄ with x = 0.1-0.7, was developed using egg-white precursors. TG measurement showed that, the precursors must be calcined at 550 °C. XRD patterns indicated the formation of single-phase cubic ferrites with particle size in the range 28.7-48.4 nm. TEM image gave particle size agrees well with that estimated using XRD. FT-IR spectroscopy showed the characteristic ferrite bands. Hysteresis loops measurements exhibited an increase in the saturation magnetization value (M_s) up to zinc content of 0.2 followed by unexpected decrease, which suggests the preference of Zn²⁺ ions to occupy octahedral sites. The decrease in the coercivity (H_c) with increasing zinc content is attributed to the lower magneto-crystalline anisotropy of Zn²⁺ ions compared to Ni²⁺ ions. Temperature dependence of the molar magnetic susceptibility (χ_M) suggested a ferrimagnetic behavior of the investigated samples and showed a decrease in the value of the Curie temperature (T_C) with increasing zinc.     

Optical properties of calcium chromate 1D-nanorods synthesized at low temperature from secondary resources

Calcium chromate 1D-nanorods have been synthesized from tannery waste solution. The solution was filtered to get rid of insoluble matters followed by addition of ammonia to precipitate calcium and chromium as hydroxide gel. The gel was heated within the temperature range 300–600 °C. At 300 °C amorphous phase of calcium chromate was formed. At 400 °C compounds of CaCrO₄, Cr₂O₃, CaCO₃ and minor amount of Mg₂CO₃(OH)₂(H₂O)₃ (Artinite) were detected. At 500 °C, CaCrO₄ compound was the major product together with traces of Cr₂O₃, CaCO₃ and MgO. At 600 °C, a crystalline compound of CaCrO₄ was formed. Nanorods of calcium chromate structured during heating associated with the crystal growth. Properties of heated products are evaluated with the help of XRD, TEM and FT-IR measurements. Optical properties of the obtained calcium chromate were estimated. A thermodynamic model of the involved reactions is suggested to explore the findings.     

Structural and optical characterization of mechanochemically synthesized copper doped CdS nanopowders

Incorporation of copper into CdS crystals has been successfully prepared by mechanical alloying using a planetary ball mill. The powders are prepared with different milling times at 300 rpm with various Cu/Cd ratios from 0.1 to 25 at%. X-ray diffraction (XRD) analysis of milled powders showed peaks corresponding to hexagonal structure with a detection of phase transition to a cubic structure with increasing milling time. Grain sizes varied from 21 to 30 nm corresponding to different Cu/Cd ratios. Field emission scanning electron microscopy (FESEM) images reveal agglomerated materials with particle size of approximately 28 nm (5 Cu at%) and layered structures caused due to the milling process. Powder composition by energy dispersive analysis of X-rays (EDAX) reveals the incorporation of copper into the CdS. Micro Raman spectroscopy showed peaks approximately at 301 and 585 cm⁻¹ corresponding to first and second order scatterings of longitudinal optical phonon mode. The LO mode at 301 cm⁻¹ shifted towards lower wave number due to decrease of grain size by increase in milling time. From high resolution transmission electron microscope (HRTEM), the dominant phase of individual CdS nanocrystals was found to be hexagonal structure along with cubic structure.     

Structural,magnetic properties,and induction heating behavior studies of cobalt ferrite nanopowders synthesized using modified co-precipitation method

Nanocrystalline cobalt ferrite CoFe₂O₄ powders have been successfully synthesized via modified co-precipitation at low temperature. Obviously, well crystalline CoFe₂O₄ phase was obtained from the precipitated precursors at pH 10 using 5?M NaOH as a base thermally treated at 80°C for 1?h in aqueous medium in the absence and the presence of 1000?ppm cetyl trimethyl ammonium bromide (CTAB) as well as sodium dodecyl sulfate (SDS) as cationic and anionic surfactants, respectively. Meanwhile, the spinel ferrite was observed with the similar conditions using ethylene glycol as an organic solvent. The microstructures of the formed powders exhibited nanospheres like structure with narrow size distribution from 6 to 10?nm. The magnetic properties of the formed cobalt ferrite powders strongly depend on the synthesis conditions. For instance, the highest saturation magnetization (M_s?=?36.2?emu/g) was achieved in the aqueous medium, whereas the lowest saturation magnetization (M_s?=?16.2?emu/g) was accomplished in the ethylene glycol medium. Indeed, heating properties of the CoFe₂O₄ samples in an alternating magnetic field (AMF) at 160?kHz were estimated. Of note, it is clear that the specific heat rate SAR values were in the range from 104.5 to 302.0?W/g at different synthesis conditions, making co-ferrite appropriate for hyperthermia treatment of cancer.     

Magnetic and semi-conducting nano-composite films of spinel ferrite and cubic zinc oxide

Magnetic and semi-conducting nano-composite films have been prepared under bias polarization, by radio-frequency sputtering of a pure zinc ferrite target. These composite thin films are made of cubic Zn_1 − yFe_yO monoxide islands inside a spinel ferrite matrix. The relative proportion of each phase depends on the substrate polarization (i.e. bias power). When no bias is applied the films solely display the diffraction pattern of a spinel phase even if some islands inside the film can be observed by electron microscopy. When the bias power is increased, the spinel phase disappears progressively as enhanced formation of islands takes place in such a manner that the cubic Zn_1 − yFe_yO monoxide is solely revealed by X-ray diffraction for a bias power higher than 5 W. From bibliographical data and calculated phase diagrams, it can be inferred that these phases would require very low oxygen partial pressure, high temperature and mechanical pressure, to be obtained simultaneously by a conventional ceramic process. This underlines the strong potential of radio-frequency sputtering of oxide targets to prepare original oxides or composite materials.     

Magnetic and catalytic properties of Cu-substituted SrFe12O19 synthesized by tartrate-gel method

Cu-substituted strontium-hexaferrites with chemical compositions SrFe_12-xCu_xO₁₉ (0 ≤ x ≤ 0.8, x  = 0, 0.2, 0.4, 0.6 and 0.8) were synthesized successfully by the tartrate-gel route, followed by calcination at 850 °C for 2 h. All the Cu-substituted compositions have single phase with hexagonal crystal structure and P6₃/mmc space group, but parent compound shows a small amount of hematite impurity phase. This suggests that introduction of Cu helps in reducing the calcination temperature to obtain a single phase compound. Furthermore, all the samples are nanocrystalline in nature with average crystallite size ranging from 40 to 50 nm. The variations in the magnetic parameters with increase in the copper content in the Sr-hexaferrite structure indicate the occupation of Cu at octahedral interstitial site. The above nanocrystalline-hexaferrite powders were employed as catalysts for the reduction of 4-nitrophenol to 4-aminophenol, in aqueous medium. The progress of the catalytic reaction was examined by UV-visible absorbance spectroscopy at different intervals of time. The results indicated that the parent compound (SrFe₁₂O₁₉) was catalytically inactive, while all other Cu-substituted samples exhibited good catalytic activities in transforming 4-nitrophenol into 4-aminophenol. Our results reveal that the catalytic property could be induced in Sr-hexaferrite samples by Cu-substitution at octahedral site.     

Magnetic properties of anisotropic Sr-La system ferrite magnets

An experiment was carried out to investigate the effect of La₂O₃ on the magnetic and physical properties of strontium ferrite magnets. It was found that the La₂O₃ addition to SrO-6Fe₂O₃ (stoichiometric composition) was very useful in stabilizing the magnetoplumbite structure and that these ferrites of the Sr-La system had excellent permanent-magnet properties. Various compositions were tested, and the optimum conditions for making magnets and some properties of typical specimens were determined. The semisintering condition was 1250°C for 1 h in oxygen, and the sintering condition 1300°C for 0.5 h in oxygen. Magnetic and physical properties are presented and discussed. The [(SrO)0.143(Fe₂O₃)_0.857]₉₈ (La₂O₃)₂ compound magnet exhibited the highest value of (BH)_max, and this value was equivalent to or higher than that of ordinary Ba and Sr ferrites     

Characterization and magnetic properties of nanocrystalline nickel ferrite synthesized by hydrothermal method

Nanocrystalline nickel ferrite has been successfully synthesized through a simple hydrothermal process at 180 °C for 10 h. The as-synthesized powders were characterized by high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) techniques. TEM image and HRTEM image revealed that the as-prepared crystals were well crystallized with grain size distribution from 50 to 80 nm. The magnetic properties were studied by vibrating sample magnetometer (VSM), it exhibited lower coercivity and higher saturation magnetization which came from high crystallinity and uniform morphologies.     

Electrical properties of Si4+ substituted copper ferrite

The electrical resistivity, , and Seebeck coefficient, , for the system Cu_1+xSi_xFe_2–2xO₄ (where x = 0.05, 0.1, 0.15, 0.2 and 0.3) have been studied as a function of temperature. Temperature variation of the resistivity exhibits two breaks. Each break is associated with a change in activation energy. The conduction process at low temperature is governed by the reaction Cu _A ¹⁺ + Cu _A ²⁺ Cu _A ²⁺ + Cu _A ¹⁺ . However, at higher temperature, it is due to intersite cation exchange and reoxidation such as Cu _A ²⁺ + Fe _B ³⁺ Cu _B ²⁺ + Fe _A ³⁺ . Measurement of the Seebeck coefficient, , from room temperature to 800 K reveals n-type conduction for the sample with x= 0.05, while the measurements for other samples show p-type conduction for lower temperatures and n-type conduction at higher temperatures. The activation energies in the paramagnetic region are found to be less than those in the ferrimagnetic region.     

Magnetic properties of Re-substituted Ni–Mn ferrite nanocrystallites

The effect of Fe³⁺ ions substitutions by rare-earth ions on magnetic properties of nanocrystalline Ni–Mn ferrite prepared by emulsion method was investigated. X-ray diffraction pattern indicated the presence of cubic structure of spinel ferrite. The crystallite sizes increased with an increase in the heat treatment temperatures, while it decreased for the substitution of rare-earth ions. The magnetic properties were changed with types of rare-earth ions and heat treatment temperatures. Room temperature Mössbauer spectra can differentiate between superparamagnetism and ferrimagnetism in nature.     

Magnetic properties of oxide nanopowders obtained by pulsed electron beam evaporation

The magnetic properties of oxide nanopowders obtained by pulsed electron beam evaporation of targets in a low-pressure gas phase have been studied. Using this method, we obtained Zn-ZnO and ZnO nanopowders with the specific magnetization amounting to 2.8 × 10⁻² and 2 G cm³/g, respectively. Significant room-temperature ferromagnetism has been observed for the fist time in a nanopowder of yttria-stabilized zirconia, where the specific magnetization reached ∼6.7 × 10⁻² G cm³/g.     

Magnetic properties and NMR studies of the SrAlM hexagonal ferrite system

The magnetic parameters for single crystals of SrAl_xFe_12−xO₁₉ (x=0, 0.8) were measured at 77 and 295 K. The nuclear magnetic resonance (NMR) experimental data of ⁵⁷Fe nuclei in domains of these samples were determined in a wide range of temperatures using the spin-echo technique. Influence of substitution of Fe³⁺ ions by Al³⁺ ions on magnetic properties have been studied with the aid of NMR spectra of ⁵⁷Fe nuclei. It is shown that only 82% of Al³⁺ exist in b-sublattice (site 2a) and 18% of Al³⁺ ions are statistically distributed in the other sublattices for SrAl_xFe_12−xO₁₉. The percentage 82% Al³⁺ in sites 2a experimentally increases the value of anisotropy constant K₁ by 0.60×10⁶ erg cm⁻³. Thus, the contribution of Fe³⁺ ion in the position 2a to the magnetic anisotropy constant of SrFe₁₂O₁₉ in low temperatures is estimated. It is shown that the value K₁(2a)=−0.90×10⁶ erg cm⁻³.     

Magnetic and electrical properties of metal/ferrite composite thin films

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Neodymium-doped copper ferrite: auto-combustion synthesis,characterization and photocatalytic properties

Neodymium doped copper ferrite nanoparticles were successfully synthesized by via a sol–gel auto combustion method with the aid of copper (II) nitrate, iron (III) nitrate, neodymium (III) nitrate and starch without adding external surfactant. Moreover, starch plays role as capping agent, reductant agent, and natural template in the synthesis CuFe_2?xNd_xO₄ nanoparticles. The as-synthesized CuFe_2?xNd_xO₄ nanoparticles were characterized by means of several techniques such as X-ray diffraction, scanning electron microscopy, energy dispersive X-ray microanalysis and UV–Vis diffuse reflectance spectroscopy. The magnetic properties of as-prepared CuFe_2?xNd_xO₄ nanoparticles were also investigated with vibrating sample magnetometer (VSM). To evaluate the photocatalyst properties of nanocrystalline CuFe_2?xNd_xO₄, the photocatalytic degradation of methyl orange (MO) under ultraviolet light irradiation was carried out.     

Magnetic properties of proximity-induced superconducting copper and silver

The magnetic properties of micrometer thick, proximity-induced superconductors have been investigated in the temperature range 5×10^–4 T _CNS T _CNS . HereT _CNS is the transition temperature of the NS proximity system. By means of ac susceptibility measurements and dc magnetization curves in copper and silver, we have determined the breakdown fieldH _b , the supercooled fieldH _sc and the superheated fieldH _sh , as functions of temperature and normal metal thicknessd _N . Precise magnetization curves of specimens withd _N <15 µm at the lowest temperatures gave the screening length as function of the field H. From these data, the spatial dependence of the local critical fieldH _c (x) and of the induced order parameter _N (x) in theN side were derived in the case _N (x)>k _B T and xK _N ^–1 . HereK _N ^–1 is the Cooper pair penetration length, andx the distance form the SN interface.     

Magnetic properties of nickel ferrite nanoparticles prepared using flotation extraction

A method has been proposed for the preparation of nickel ferrite nanoparticles in a system of direct sodium dodecyl sulfate micelles using ion flotation. Amorphous nickel ferrite nanoparticles with the overall composition xNiFe₂O₄ · yFe₂O₃ · zH₂O, containing dodecyl sulfate anion impurities, have been prepared. According to transmission electron microscopy results, the size distribution of the synthesized nanoparticles has a maximum in the range 4 to 6 nm, and the ferrite is X-ray amorphous. The blocking temperature of the synthesized nanoparticles is 25 K. The ferrite possesses superparamagnetic properties, with a specific saturation magnetization of 15 A m²/kg at 5 K.