Magnetic transitions and electrical transport in Bi-doped lanthanum strontium manganites

The temperature dependence of the electrical resistivity ρ, thermoelectric power S and the magnetic susceptibility χ of La₀.₇–xBixSr₀.₃MnO₃ (x = 0.05, 0.10, and 0.15 at.%) manganites were investigated. La₀.₇–xBixSr₀.₃MnO₃ crystallizes in a single phase rhombohedral structure with parasitic phase inclusions. With increasing Bi concentration, a systematic decrease in the ferromagnetic transition temperature (TC), the metal–semiconducting transition temperature (Tms1) and also the values of activation energies Eρ and ES from ρ(T) and S(T) were observed. On the other hand, in the high-temperature (T > Tms) paramagnetic semiconductor regime, the adiabatic small polaron hopping model fit well, thereby indicating that polaron hopping might be responsible for the conduction mechanism. In addition, the thermoelectric power data at low temperatures were analyzed by considering both the magnon and the phonon drag concept, while the high-temperature data were confirmed a small polaron hopping conduction mechanism

Magnetic spectra analysis of dielectrics

Method of magnetic spectroscopy is used to analyze and to interpret the experimental data obtained by magnetic measurement of the complex permeability spectra of Mg ferrite and NiZn ferritepolymers. Ferritepolymers were prepared from various concentration of NiZn ferrite particles as a soft magnetic fillers dispersed in PVC polymer matrix. Effect of the filler content on the permeability spectra of NiZn ferritepolymers was examined and compared with presented sintered ferrite samples. The variations of permeability and relaxation frequency due to ferrite filler concentration in composite are presented and discussed from point of view the magnetization processes in samples

Magnetic transitions and electrical transport in Bi-doped lanthanum strontium manganites

The temperature dependence of the electrical resistivity ρ, thermoelectric power S and the magnetic susceptibility χ of La₀.₇–xBixSr₀.₃MnO₃ (x = 0.05, 0.10, and 0.15 at.%) manganites were investigated. La₀.₇–xBixSr₀.₃MnO₃ crystallizes in a single phase rhombohedral structure with parasitic phase inclusions. With increasing Bi concentration, a systematic decrease in the ferromagnetic transition temperature (TC), the metal–semiconducting transition temperature (Tms1) and also the values of activation energies Eρ and ES from ρ(T) and S(T) were observed. On the other hand, in the high-temperature (T > Tms) paramagnetic semiconductor regime, the adiabatic small polaron hopping model fit well, thereby indicating that polaron hopping might be responsible for the conduction mechanism. In addition, the thermoelectric power data at low temperatures were analyzed by considering both the magnon and the phonon drag concept, while the high-temperature data were confirmed a small polaron hopping conduction mechanism

Investigation of two-stage magnetic Barkhausen noise measurement method at power line frequency

The aim of the paper was to study the features of measurement of the magnetic Barkhausen noise by the new two-stage method in the high excitation frequency region (power line frequency). The magnetic Barkhausen noise was investigated on grain oriented Fe-3%Si steel subjected to different heat treatment. By application of an air coil on the output of the power amplifier we were able to linearize the excitation field. At the same time, the air coil suppressed the unwanted noise from the output of the power amplifier. We have found that the two-stage method is able to reveal a peak of the power spectrum even if it is located at low frequency, in contrast to the classical one-stage method. Further, we successfully applied a model of the power spectrum to the real magnetic Barkhausen noise obtained from the two-stage measurement

Electromagnetic properties of selected hexaferrites

Ba(Sr)(Me12+Me24+)xFe12-xO19 hexagonal ferrites preparation with substitution ratio of 0.0 x 0.6. The iron ionswere substituted by selected cation combinations (divalent Me12+= Ni, Zn, Sn, Co and tetravalent Me24+= Ti, Zr, Ru ions).The samples were synthesised by high energy milling and metallorganic precursor method. A special attention was focused toresults obtained for (ZnTi)x substitutions.. The changes of coercivity HC were chosen as a evaluation criterion of anisotropyvariation. Simultaneously with the magnetic properties, the dielectric parameters were also tested. Two dielectric relaxationprocesses were detected in Ba - Sr ferrite. Our results showed probably a ferroelectric behaviour of some ferrite samples

Microstructural and magnetic characteristics of divalent Zn, Cu and Co-doped Ni ferrites

Divalent zinc, copper and cobalt doped nickel ferrites with the chemical formula Ni_{1-x-y-z}Zn_{x}Cu_{y}Co_{z}Fe₂O₄ where x values ranging from 0.4 to 0.6, y=0.1, z=0.01 and 0.02 have been synthesized by conventional ceramic method. The effect of Zn²⁺, Cu²⁺ and Co²⁺ ions substitution on the selected microstructural and magnetic characteristics have been investigated to examine the utility of prepared ferrite materials for high-frequency applications. X-ray diffraction measurements confirmed the single-phase spinel cubic structure in all the samples and modifications in lattice parameter according to the ionic radii size of doped ions. The net magnetic moment, given by the differences between the magnetic moments of A and B sublattice, increased with raising substitution of Ni²⁺ ions. The measured frequency dispersion of complex permeability was discussed in terms of the changes in chemical composition, microstructure and the associated processes of resonance and/or relaxation due to domain wall movements and damping of spin rotations contributing to the fall of permeability and rise of magnetic losses

Magnetic Properties of Yttrium-Substituted NiZn Ferrites

Polycrystalline NiZn ferrite doped with a small amount of $Y^{3+}$ ions and having the composition of $Ni_{0.42}Zn_{0.58}Y_{x}Fe_{2-x}O_{4}$, where x=0.00, 0.01, 0.02, 0.04, 0.06, 0.08 and 0.10, was analyzed. Specimens were prepared by the ceramic method. Thermo-magnetic analysis and evaluation of hysteresis loops parameters were chosen as main examination methods in this study. Various parameters, such as Curie temperature $T_{C}$, coercive field $H_{c}$, remanent magnetic flux density $B_{r}$, hysteresis loop area and amplitude/initial permeability were studied at low frequencies

Nickel/Zinc ratio and lanthanum substitution effect on structural and magnetic properties of nickel zinc ferrites

Improvement of NiZn ferrites properties by means on Ni/Zn content ratio modification and by partial substitution of Fe³⁺ ions by La³⁺ ions is presented. Ni_{x}Zn_{1-x}Fe₂O₄ and Ni_{x}Zn_{1-x}La_{0.02}Fe_{1.98}O₄ samples of small particles were prepared by self-propagated combustion method. X-ray spectroscopy was used for structural analysis, temperature dependence of magnetic susceptibility was used for evaluation of chemical and phase composition. Analysis showed that pure spinel structure without secondary phase caused by La ions for all values of Ni/Zn content was present. Noticeable growth of the magnetic susceptibility at room temperature was observed with rising of Zn²⁺ ions content

Magnetic Properties of Ni0.3Zn0.7Fe2O4Ni_{0.3}Zn_{0.7}Fe_2O_4 Ferrites with Iron Ions Partly Substituted by Europium

This work is devoted to the study of the impact of the substitution of iron by Eu on the properties of magnetically soft $Ni_{0.3}Zn_{0.7}Eu_{x}Fe_{2-x}O_4$ ferrites aimed at enhancement of the knowledge related to the behavior of such materials in dependence on the amount of iron substitution. Our latest studies focused on the materials having similar chemical composition gave a hint of some possible approaches to manage the resulting magnetic properties in a precisely controlled way by the combination of several factors; choice of initial chemical composition of non-substituted ferrite, selection of substituted and substituting element, variations of final chemical composition, modifications of fabrication technology (sintering temperature and time), etc