Synthesis of hollow ferrite nanospheres for biomedical applications

Hollow ferrite spheres of 220-340 nm diameter were synthesized at 60 °C as multi-functionalized magnetic carriers which are potentially applicable both as drug delivery systems (DDS) and hyperthermia treatment. We found that SH and OH groups on the silica template spheres enabled the fabrication of continuous ferrite shells of 20-30 nm in thickness. Transmission electron microscopy and energy-dispersive spectroscopy revealed that the templates were dissolved by a NaOH solution, yielding hollow particles exhibiting saturation magnetization of 78 emu/g. The results suggested that the ferrite shells are porous and the pores work as pathway for releasing drugs from the hollow particle inside.     

Abnormal morphology of nanocrystalline Mn–Zn ferrite sintered by pulse electric current sintering

Nanocrystalline manganese–zinc (Mn–Zn) ferrite powders prepared by the sol–gel auto-combustion method are sintered to form bulk ferrite by pulse electric current sintering technique. The sample phase, before sintering and after sintering, is carried out by X-ray diffraction (XRD). The morphology of the sample is observed by scanning electron microscopy (SEM). The results indicate that the bulk ferrite obtained has a pure spinel structure. With special graphite die, a special morphology is observed, which is explained by pressure, temperature and induced electromagnetic field.     

Synthesis and characterizations of microwave sintered ferrite powders and their composite films for practical applications

Phase pure single phase ferrite powders of (Ni_xR_1−x)_0.5Zn_0.5Fe₂O₄ (R=Mn, Co, Cu; x=0, 0.5) were manufactured using microwave sintering at 930 °C for 10 min in air atmosphere. The powders were characterized for their structure, microstructure, thermal, and magnetic properties. Selected powders were used as fillers to prepare their composite films using polymethyl methacrylate polymers as matrix. The composite films were prepared using the melt blending approach and were tested for their microstructure, thermal, and magnetic hysteresis loop as well as 3D magnetic field space mappings using an electromagnetic compatibility scanner. Among the studied ferrites, cobalt doped ferrites and their composites showed the best electromagnetic interference (EMI) shielding effectiveness value and have potential for practical EMI shielding applications.     

Synthesis and magnetic properties of Mn–Zn ferrite nanoparticles

Mn–Zn ferrite nanoparticles (Mn_1−xZn_xFe₂O₄) are synthesized by a hydrothermal precipitation approach using metal sulfate solution and aqueous ammonia. The analysis methods of XRPD, TEM, TGA, and VSM are used to characterize the magnetic nanoparticles. Through the characterization of the precipitated nanoparticles, the effects of the reacting component proportions and preparation techniques on the Curie temperature, the magnetization, and the size distribution of Mn–Zn ferrite nanoparticles are discussed. Furthermore, the Mn–Zn ferrite nanoparticles are used to prepare ferrofluid. Variation of the magnetic properties of the ferrite nanoparticles with the composition content x of Zn and the magnetic moment of the nanoparticles are discussed.     

Synthesis and characterization of carboxymethyl dextran-coated Mn/Zn ferrite for biomedical applications

Previous studies have shown that magnetic nanoparticles possess great potential for various in vivo applications such as magnetic resonance imaging contrast enhancement, tissue repair, cancer treatment agents, and controlled drug delivery. Many of these applications require that magnetic nanoparticles be colloidally stable in biological media. The goal of this study was to obtain a magnetic fluid produced by the colloidal suspension of manganese/zinc ferrite (MZF) nanoparticles that could be stably dispersed in aqueous solution throughout the range of physiological pH and ionic strength. These superparamagnetic nanoparticles were stabilized through steric repulsion by coating with biologically compatible carboxymethyl dextran (CMDx). Samples of the resultant magnetic fluid were analyzed using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), X-ray diffraction (XRD), zeta potential measurements, dynamic light scattering, transmission electron microscopy (TEM), and SQUID magnetometry. Results show that we obtained superparamagnetic metal-oxide crystals with composition of Mn_0.24Zn_0.76Fe₂O₄. Cell viability measurements show the material is non-toxic to MCF-7 and CaCo-2 cell lines at concentrations of up to 7.5 mg/mL of particle fraction for contact time of up to 48 h.     

Magnetic properties of substituted strontium ferrite nanoparticles and thin films

SrFe_12−x(Zr_0.5Mg_0.5)_xO₁₉ nanoparticles and thin films with x=0-2.5 were synthesized by a sol-gel method on thermally oxidized silicon wafer (Si/SiO₂). Structural and magnetic characteristics of synthesized samples were studied employing x-rays diffraction (XRD), transmission electron microscopy (TEM), magnetic susceptometer, atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM), and vibrating sample magnetometer (VSM). TEM micrographs display that the narrow size distribution of ferrite nanoparticles with average particle size of 50 nm were fabricated. Fitting obtained data of effective magnetic susceptibility by Vogel-Fulcher law confirms the existence of strong magnetic interaction among fine particles. XRD patterns and FE-SEM micrographs demonstrated that single phase c-axis hexagonal ferrite films with rather narrow grain size distribution were obtained. AFM micrographs exhibited that the surface roughness increases with an increase in Zr-Mg content. It was found from the VSM graphs that with an increase in substitution contents the coercivity decreases, while the saturation of magnetization increases. The Henkle plots confirms the existence of exchange coupling among nano-grain in ferrite thin films.     

Correlation between site preference and magnetic properties of substituted strontium ferrite thin films

SrFe_12−x(Sn_0.5Zn_0.5)_xO₁₉ thin films with x=0−5 were synthesized by a sol-gel method on thermally oxidized silicon wafer (Si/SiO₂). The site preference and magnetic properties of Zn-Sn substituted strontium ferrite thin films were studied using ⁵⁷Fe Mössbauer spectroscopy and magnetic measurements. Mössbauer spectra displayed that the Zn-Sn ions preferentially occupy the 2b and 4f₂ sites. The preference for these sites is responsible for the anomalous increase in the magnetization at high Zn-Sn substitutions. X-ray diffraction (XRD) patterns and field emission scanning electron microscope (FE-SEM) micrographs demonstrated that single phase c-axis hexagonal ferrite films with rather narrow grain size distribution were obtained. Vibrating sample magnetometer (VSM) was employed to probe magnetic properties of samples. The maximum saturation of magnetization and coercivity at perpendicular direction were 265 emu/g and 6.3 kOe, respectively. It was found that the complex susceptibility has linear variation with static magnetic field.     

Minimizing of power loss in Li-Cd ferrite by nickel substitution for power applications

The effect of Ni substitution on the microstructure, dielectric, impedance, magnetic and power loss properties has been investigated on a series of Li_0.35-0.5xCd_0.3Ni_xFe_2.35-0.5xO₄ (0.00≤x≤0.08) ferrite prepared by citrate precursor method. Dielectric and impedance measurements have been determined in the frequency range 100 Hz-10 MHz. An enhancement in permittivity was observed with Ni concentration and exhibits the maximum value of ∼7×10³ for x=0.02 sample. The impedance spectroscopy technique has been used to study the effect of grain and grain boundary on the electrical properties of all the samples. Power loss measurements have been carried out in the frequency range 50 kHz-5 MHz at induction condition of B=10 mT. Power loss has been found to be quite low, less than 100 kW/m³ up to 500 kHz, with the substitution of Ni in Li_0.35-0.5xCd_0.3Ni_xFe_2.35-0.5xO₄ ferrite, which is useful for technological aspects.     

Magnetic properties and DC electrical resistivity studies on cadmium substituted nickel-zinc ferrite system

Polycrystalline Ni_0.65−xCd_xZn_0.35Fe₂O₄ ferrites with x varying from 0.00 to 0.20 in steps of 0.04 have been prepared by conventional ceramic route. Calcination and sintering of samples were performed at 950 and 1250 °C for 4 and 2 h, respectively. The prepared samples were characterized by powder X-ray diffraction. The observed modifications in structure and increase in lattice constant are attributed to the difference in ionic radius of substituted Cd²⁺ ion and displaced Ni²⁺ ion. The room temperature specific saturation magnetization and Curie temperature are observed to decrease continuously with decrease in cadmium content and are attributed to the decline of A-B exchange interaction. The monotonic increase in initial permeability and decrease in magnetic loss are observed with cadmium concentration. An increase in dc electrical resistivity is observed up to x=0.12 of cadmium followed by a continuous decrease. The variation of electrical resistivity with temperature was measured in the temperature range of RT-140 °C and the corresponding activation energies for conduction obtained from the log ρ vs 1/T graphs.     

Cationic behavior and the related magnetic and magnetotransport properties of manganese ferrite thin films

Manganese ferrite (Mn_xFe_3−xO₄) thin films have been prepared by a sol–gel method. The samples (x≤1.25) are polycrystalline containing well-defined grains and maintain cubic spinel structure with increasing lattice constant with x. The substituting Mn ions were found to have multi-valence, +2 and +3, by X-ray photoelectron spectroscopy. The saturation magnetization of the Mn-substituted films measured by vibrating sample magnetometry was found to increase from that of Fe₃O₄ at low x and then gradually decreases as x increases further. Such magnetic behavior can be explained in terms of the dominance of Mn²⁺ species over Mn³⁺ at low x and the gradual decrease in the population ratio Mn²⁺/Mn³⁺ as x increases. The observed decrease in the coercivity with increasing x implies the increase in octahedral Mn²⁺ population. The Mn-substituted samples exhibit magnetoresistance (MR) effect the maximum intensity of which is gradually reduced with x from that of Fe₃O₄. All samples show increasing MR with increasing external field (H), while their magnetization curves start to saturate near H=2 kOe. Such increasing MR with H can be explained in terms of the tunneling of spin-polarized carriers across grain boundaries. The reduction in the MR intensity with x can be partly explained in terms of the decrease in spin-polarized carrier density associated with octahedral occupation of Mn²⁺ ions.     

High permeability and low power loss of Ti and Zn substitution lithium ferrite in high frequency range

The effect of Zn and Ti on the magnetic, power loss and structural properties of Li_0.5Zn_xTi_xMn_0.05Fe_2.45−2xO₄ ferrites (x=0.0 to 0.30 in step of 0.05)+0.5 wt% Bi₂O_3, prepared by standard ceramic technique, has been investigated. Complex permeability (μ*=μ′−jμ″) has been analyzed at room temperature in frequency range from 1 to 10³ MHz. It was found an enhancement in permeability with Ti and Zn concentration in Li_0.5Zn_xTi_xMn_0.05Fe_2.45−2xO₄ and exhibits the maximum value 106 for x=0.20 sample. Complex permeability of these ferrites exhibits stable frequency response up to 7 MHz beyond which the real part decreases sharply and imaginary part increases to have a peak at the relaxation frequency. Power loss measurements have been carried out in induction condition (B=10 mT) in frequency range of 50 kHz to 3 MHz. Power loss has been found to be quite low with the substitution of Ti and Zn in lithium ferrite.     

Electromagnetic and microwave absorption properties of Fe3O4 magnetic films plated on hollow glass spheres

Magnetic hollow spheres of low density were prepared by plating Fe₃O₄ magnetic films on hollow glass spheres using ferrite plating. The complex permeability and permittivity of spheres–wax composites were measured in the range of 2–18 GHz. The complex permeability and permittivity increased, and the dielectric and magnetic losses were improved as the volume fraction of the magnetic spheres in the composites increased from 60% to 80%, which also resulted in a great improvement of microwave absorption properties. For composites with volume fraction 80%, its magnetic resonance frequency was at about 13 GHz and it appeared three loss peaks in the calculated reflection loss curves; the bandwidth less than −10 dB was almost 4 GHz which was just in the Ku-band frequencies (12–18 GHz) and a minimum reflection loss of −20 dB was obtained when the thickness was 2.6 mm; the microwave absorbing properties were mainly due to the magnetic loss. The results showed that the magnetic spheres composites were good and light microwave absorbers in the Ku-band frequencies.     

Preparation and characterization of ZnSn-substituted barium ferrite thin films

The preparation of ZnSn-substituted barium ferrite films by sputtering deposition was studied. The as-sputtered films were amorphous, and annealing at a minimum of 750 °C was required to crystallize the films, based on the X-ray diffraction analysis and the magnetic measurements. Scanning electron microscopy combined with energy-dispersive X-ray spectroscopic microanalysis confirmed that the films were single phase with the composition BaZn_xSn_xFe_12−2xO₁₉, x=0.2−0.3, and their thicknesses were 0.4-1.0 μm when annealed at 750-900 °C. Atomic and magnetic force microscopy studies showed no significant grain growth upon annealing and that the films consisted of single-domain grains forming interaction-cluster-type domains. The natural ferromagnetic resonance frequency was determined at around 4 GHz, together with substantial magnetic losses that make these films promising candidates for microwave absorbers.     

Preparation and microwave absorption properties of electroless Co-Ni-P coated strontium ferrite powder

A new type of Co-Ni-P coated strontium ferrite nanocomposite was prepared with electroless plating enhanced by ultrasonic wave at room temperature. The plating process was studied carefully. The morphology, crystal structure and microwave absorption properties of the Co-Ni-P coated powder were studied with field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), energy dispersive analysis of X-rays (EDX) and vector network analyzer. The results show that the strontium ferrite powder was successfully coated with Co-Ni-P alloy and possesses excellent microwave absorption properties. The maximum microwave loss of the composite powder reaches −44.12 dB. The bandwidth with the loss above −10 dB exceeds 13.8 GHz.     

Effect of annealing conditions on structural and magnetic properties of laser ablated copper ferrite thin films

The effect of annealing conditions on structural and magnetic properties of copper ferrite thin films on (100) Si substrates was examined in detail. After deposition, the ferrite thin films were post-annealed in vacuum and in oxygen atmosphere for several hours. It is found that the crystal structure of CuFe₂O₄ thin films changed drastically depending on different heating process. A maximum magnetization was achieved in the film that was vacuum annealed and it decreased remarkably after oxygen annealing.     

The role of nickel addition and annealing temperature on ion storage performance of nanostructured nickel ferrite thin films

The sol–gel spin-coated nickel ferrite (NF), NiFe₂O₄, thin films were synthesised and the effect of annealing temperature and compositional ratio on different properties of samples were investigated. Electrochemical performance of the films was measured in the presence of KOH and LiClO₄/PC electrolyte. Generally, addition of nickel increases the current density. The NF thin films with molar ratio of 0.5 and annealed at 400 °C have the highest charge density value and the highest capacitance in both electrolytes. Annealing temperature had significant effect on electrochemical properties of NF thin films and the diffusion coefficient enhanced by increasing the annealing temperature. X-ray diffraction patterns of prepared samples showed the rhombohedral structure, hematite phase (α-Fe₂O₃), of iron oxide sample and the presence of inverse spinel structure confirms the formation of NF. Field emission scanning electron microscopy images revealed that the morphology of films changes from larvae shape to granular structure by nickel incorporation and the grain size increased by raising the annealing temperature. The absorption edge of the hematite shift to higher wavelength by annealing and nickel incorporation and band gap narrowing has been occurred.     

The role of copper ions on the structural and magnetic characteristics of MgZn ferrite nanoparticles and thin films

In this study Cu_xMg_0.5−xZn_0.5Fe₂O₄ (x=0-0.5) nanoparticles and thin films were prepared by sol-gel processing. The morphologies of nanoparticles were observed by transmission electron microscope (TEM). The Mössbauer spectroscopy (MS) was employed to determine the site preference of the constitutive elements. Magnetic dynamics of the nanoparticles was studied by the measurement of AC magnetic susceptibility versus temperature at different frequencies. The phenomenological Néel-Brown and Vogel-Fulcher models were employed to distinguish between interacting or non-interacting system. Results exhibited that there is strong interaction between fine particles. X-ray diffraction (XRD) patterns of the thin films indicate the formation of single-phase cubic spinel structure. Atomic force microscope (AFM) was employed to evaluate the surface morphologies of the prepared thin films. Vibrating sample magnetometer (VSM) was employed to probe magnetic properties of samples. It was found that with an increase in the amount of copper, the saturation of magnetization and initial permeability increase.     

高矫顽力和大矩形比钡铁氧体垂直磁记录薄膜

用对向靶直流溅射系统制备了c轴垂直取向的钡铁氧体薄膜.用少量的Al来取代Fe,从而制备了成分为BaAlxFe12-xO19(x=0,1,2)的钡铁氧体薄膜.研究了Al取代Fe对其结晶学性能、磁学性能的影响.研究了退火效应及基板温度对薄膜性能的影响.获得了c轴垂直取向的具有高矫顽力和大矩形比的钡铁氧体薄膜 关键词： 钡铁氧体薄膜 铝取代 高矫顽力 大矩形比     

Study of NiCuZn ferrite powders and films prepared by sol gel method

This paper reports that a series of NiCuZn ferrite powders and films are prepared by using sol-gel method.The effects of raw material composition and the calcinate temperature on magnetic properties of them are investigated.The NiCuZn ferrite powders are prepared by the self-propagating high-temperature synthesis method and subsequently heated at 700 C～1000 C.The results show that NiCuZn ferrite powders with single spinel phase can be formed after heat-treating at 750 C.Powders obtained from Ni 0.4 Cu 0.2 Zn 0.4 Fe 1.9 O 4 gel have better magnetic properties than those from gels with other composition.After heat-treating at 900 C for 3 h,coercivity H c and saturation magnetization M s are 9.7 Oe (1 Oe=80 A/m) and 72.4 emu/g,respectively.Different from the powders,NiCuZn films produced on Si (100) from the Ni 0.4 Cu 0.2 Zn 0.4 Fe 2 O 4 gel formed at room temperature possess high properties.When heat-treating condition is around 600 C for 6 min,samples with low H c and high M s will be obtained.The minimal H c is 16.7 Oe and M s is about 300 emu/cm 3.In comparison with the films prepared through long-time heat treating,the films prepared through short heat-treating time exhibits better soft magnetic properties.     

Remarkable influence on the dielectric and magnetic properties of lithium ferrite by Ti and Zn substitution

The effect of Zn and Ti substitution on the magnetic and electrical properties of Li_0.5Zn_xTi_xMn_0.05Fe_2.45−2xO₄ ferrites (x=0.0 to 0.30 in steps of 0.05) +0.5wt% Bi₂O₃ prepared by a standard ceramic technique has been investigated. Electrical conductivity and dielectric measurements at different temperatures from 300 K to 700 K in the frequency range from 100 Hz to 2 MHz have been analysed. The variation of the real part of dielectric constant (ε^′) and loss tangent (tanδ) with frequency and temperature has been studied; it follows the Maxwell–Wagner model based on the interfacial polarization in consonance with the Koops phenomenological theory. It is found that the permittivity of zinc and titanium substituted lithium ferrite improves and shows a maximum value ( 1.5×10⁵) at 100 Hz for the x=0.25 sample. The dielectric transition temperature (T_d) depends on the concentration of Ti and Zn in Li_0.5Zn_xTi_xMn_0.05Fe_2.45−2xO₄. The saturation magnetization and Curie temperature both decrease with increase in the concentration of Ti and Zn in the ferrite.