O. F. Caltun

Study of the microstructure and of the permeability spectra of Ni–Zn–Cu ferrites

Abstract Microstructure and magnetic properties of Ni–Zn ferrite are highly sensitive to the preparation methodology, sintering conditions and to the amount of constituent metal oxides, impurities or doping levels. This paper focuses its discussion on dependence of permeability spectra on the frequency for samples of Ni–Zn–Cu ferrite sintered at different temperatures. The experimental and calculated complex permeability curves are compared.

Magnetic properties of high frequency Ni-Zn ferrites doped with CuO

Cu substituted Ni-Zn ferrites, with different copper content, were prepared by a conventional ceramic technique. Structural and magnetic properties of the ferrites were characterized by X-ray diffraction, scanning electron microscopy, frequency dependent power loss, and high frequency (10/sup 6/-10/sup 9/ Hz) permeability measurements. These studies revealed that the magnetic performances increase considerably with the optimum concentration of the additions. The contribution of two magnetization mechanisms, domain wall motion and magnetization rotation, on the high frequency complex permeability, is also discussed.

Differential phenomenological models for the magnetization processes in soft MnZn ferrites

Jiles-Atherton, Hodgdon, and Preisach models have been used to simulate the magnetization processes measured for soft MnZn ferrite cores. Magnetization curves that were not used in the identification are calculated. The differences between the results of the simulations and the experimental data are discussed.

Structural and Magnetic Characterizations of Coprecipitated Ni–Zn and Mn–Zn Ferrite Nanoparticles

Two mixed ferrite systems, namely Ni0.65Zn0.35 Fe2O4 (Ni-Zn) and Mn0.75 Zn0.18 Fe2.07 O4 (Mn-Zn) have been prepared by coprecipitation method, and then the resulting ultrafine powders were heat treated at different temperatures from 200 to 800degC for improved crystallinity and magnetic properties. The samples were characterized by X-ray diffraction, vibrating sample magnetometry, and ferromagnetic resonance spectrometry. As a result of the heat treatment, the average particle size has been found to increase from 9.9 to 15.7 nm for Ni-Zn ferrites and from 2.4 to 10.2 nm for Mn-Zn ferrites, and the corresponding magnetization values have increased from 9.1 to 23 emu/g for Ni-Zn ferrites and from 7.9 to 11.7 emu/g for Mn-Zn ferrites, respectively. The results are discussed in the light of changes in particle size and inversion degree parameter for cationic distribution at nanoscales

Differential Preisach model for the description of dynamic magnetization processes

A differential dynamic Preisach model developed by us and introduced as an idea suggested by Bertotti is generalized. The starting point of this model is that the instantaneous excess field due to the moving and dynamic processes can be approximated as a function of M and it’s variation rate dM/dt: F(M,dM/dt). Thus, we determine a differential equation for the magnetic susceptibility. The model’s parameters are found by an original identification method. As an application we simulate a simple electrical circuit and compare the results with the experimental data. A very good agreement between the measured and simulated data is observed.

Losses and magnetic properties of Bi2O3 doped MnZn ferrites

Abstract The experimental set-up allows to store the measured data and the energy losses per cycle are calculated. The experimental results are compared with the simulated ones obtained in the dynamic Preisach model. The influences of the Bi 2 O 3 content and of the excitation frequency on the magnetic properties are discussed; an optimum amount of impurities is found.

The influence of the chelating/combustion agents on the structure and magnetic properties of zinc ferrite

AbstractThe present study is reporting the influence of the chelating/combustion agents on the magnetic properties of Zn ferrite. Six chelating/combustion agents, citric acid, egg white, tartaric acid, glycine, glucose and urea, were used to obtain monophase zinc nanoferrite via a sol-gel auto-combustion method. The samples were subjected to a comparative study of structural features and magnetic properties by means of infrared spectroscopy, X-ray diffractometry, scanning electron microscopy and vibrating sample magnetometry. Significant influence of fuel and combustion mode was observed in the magnetic behavior of as-obtained samples. Values of the structural parameters were discovered to vary as a function of fuel choice, and to obtain crystallite size between 38 and 62 nm, inversion degree between 0.239 and 0.807, lattice parameter between 8.4125 and 8.4432 Å. The optimization of sol-gel method synthesis of zinc ferrite nanoparticles by chosing the appropriate fuel is providing structural and magnetic properties of zinc nanoferrite as potential materials to be used in biomedical applications.

Magnetic Measurements of RE-Doped Cobalt Ferrite Thin Films

Cobalt ferrite is a ferrimagnetic material with properties which support its use in different types of devices. In bulk form CoFe2O4 presents the highest magnetostriction coefficient relative to other ferrites making it a good candidate for sensors and actuators. Due to the industries miniaturization trend, several research groups focused their study on obtaining novel thin films with high magnetostriction coefficient. The aim of this work was to investigate the influence of the substrate temperature and rare earth addition on the properties of cobalt ferrite thin films deposited by pulsed laser deposition. CoFe2O4, CoFe1.8Gd0.2O4 and CoFe1.8La0.2O4 thin films were deposited using an Nd-YAG laser (532 nm) with a 10 Hz repetition rate and 10 ns pulse duration. The target-substrate distance of 2.5 cm and laser fluence of 10 J/cm2 were kept constant. The substrate temperature was varied from 200 °C to 600 °C. The structural properties of the thin films obtained by Raman spectroscopy and scanning electron microscopy indicated the formation of a single cobalt ferrite structure. Hysteresis loops for both in-plane and out-of-plane configuration were obtained using a vibrating sample magnetometer. These results showed an increase in coercive field and maximum magnetization as the substrate temperature was raised from 200 °C to 400 °C. Vibrating sample magnetometer measurements of the cobalt ferrite thin film deposited at 400 °C revealed a tendency of the particles to a perpendicular magnetic arrangement.

Characterization of vacuum evaporated In - Se thin films

The InSe films of different thicknesses (290–730 mm) were deposited onto glass substrates under a pressure of 3×10−5 Torr by vacuum evaporation method. The composition (In=53.50%, Se=46.50%) of this film was confirmed using Auger Electron Spectroscopy (AES). Thicknesses of the deposited films have been measured using a Multiple Beam Interferometry. The amorphous nature of the film is confirmed with X-ray diffractogram. From the transmittance spectra in the range of 500 nm-1200 nm, it is observed that the film showed direct allowed transition. Effect of thickness on the optical parameters such as the fundamental band gap, absorption constant, refractive index of InSe thin films are reported. Under low electric field (∼ 1.5×105 Vcm−1), the results of DC conductivity measurements revealed that the variable range hopping is the dominant conduction mechanism. The values of localized states density, localization radius and hopping energy of this film are estimated as 5.57×1020 cm−3eV−1, 0.84 Å and 0.247 eV, respectively.

Magnetic nanoparticles for medical applications: Progress and challenges

Magnetic nanoparticles present unique properties that make them suitable for applications in biomedical field such as magnetic resonance imaging (MRI), hyperthermia and drug delivery systems. Magnetic hyperthermia involves heating the cancer cells by using magnetic particles exposed to an alternating magnetic field. The cell temperature increases due to the thermal propagation of the heat induced by the nanoparticles into the affected region. In order to increase the effectiveness of the treatment hyperthermia can be combined with drug delivery techniques. As a spectroscopic technique MRI is used in medicine for the imaging of tissues especially the soft ones and diagnosing malignant or benign tumors. For this purpose ZnxCo1−xFe2O4 ferrite nanoparticles with x between 0 and 1 have been prepared by co-precipitation method. The cristallite size was determined by X-ray diffraction, while the transmission electron microscopy illustrates the spherical shape of the nanoparticles. Magnetic characterizations of t...