Powder ferromagnetic resonance spectra of some mixed ferrites
TL;DR: In this paper, the effect of the internal fields on the linewidths and the resonance fields of six ferrites at 9.1 GHz in the temperature range 25 to 290°C was studied.
Abstract: The powder FMR of six ferrites at 9.1 GHz in the temperature range 25 to 290° C is reported in this paper. The effect of the internal fields on the linewidths and the resonance fields are studied. Curie temperatures obtained for some of the ferrites from FMR are compared with the values obtained from an oscillator technique. The line shapes are found to be of Lorenzian shape. Effectiveg values were calculated and a brief discussion is made about the various contributions to the total field.
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TL;DR: In this paper , the co-precipitation of Mn ferrite (Mn x Fe 3-x O 4 , x = 0.0, 0.6, and 0.8) has been successfully demonstrated using the organic base ethanolamine as the chelating agent.
57 citations
TL;DR: In this paper, the magnetic and dielectric spectra of hybrid polymer composites are studied in the frequency range from 1MHz to 10GHz, and the development of a core-shell structure is evidenced by the lower electric percolation threshold in an HPC compared with that in PU filled with conductive filler.
Abstract: Polymer composites (PCs) with a polyurethane (PU) matrix filled with magnetic filler (MnZn ferrite) and hybrid polymer composites (HPCs) consisting of this magnetic filler and various types of conductive fillers (carbon black, carbon fibers, aluminum powder, polypyrrole) are prepared. The matrix structure of a HPC is formed (i) by a polymer filled with conductive filler, which forms the skeleton of an infinite cluster, and (ii) by ferrite particles that are larger than conductive particles. Thus, an HPC represents an ensemble of ferrite particles each of which is surrounded by a conductive medium and can be considered as a “core–shell” structure. The development of a core–shell structure is evidenced by the lower electric percolation threshold in an HPC compared with that in PU filled with conductive filler. Magnetic and dielectric spectra of PCs and HPCs are studied in the frequency range from 1 MHz to 10 GHz. Hybrid systems exhibit a considerable enhancement of magnetic losses compared with PCs. The enhancement of magnetic losses in HPCs is due to the conduction currents that are induced in the conductive shell by a microwave magnetic field.
44 citations
TL;DR: In this paper, the ESR spectra of the ferrite system Co 0.6 Zn 0.4 Mn x Fe 2− x O 4 (x = 0, 0.1, 0 2, 0.2, 0 3, 0 4, 0 5, 0 6, 0 7, 0 8, 0 9, 0 10, 0 11, 0 12, 0 13, 0 14, 0 15, 0 16, 0 17, 0 18, 0 19, 0 20, 0 21, 0 22, 0 23, 0 24, 0 25,
33 citations
TL;DR: In this paper, magnetic glass-ceramics with the W-type (BaFe18O27) hexagonal Ba-ferrite as a prominent crystalline phase have been prepared from glasses in the system by subjecting the latter to a two stage heat-treatment.
28 citations
TL;DR: In this paper, the effect of different concentration of Ce ions on the magnetic properties of nickel ferrite nanoparticles is discussed, and the results are explained in terms of a magnetic moment obtained by a vibrating sample magnetometer.
Abstract: In the present work, effect of different concentration of Ce ions on the magnetic properties of nickel ferrite nanoparticles is discussed. A series of NiCe
x
Fe2−x
O4 (x=0.0–0.10) samples were prepared by a chemical route. XRD patterns show that all the samples are in pure spinel phase except that with x=0.10. This indicates that rare earth ions have limited solubility in the spinel lattice. Magnetic properties are studied by electron paramagnetic resonance spectroscopy (EPR) and the results are explained in terms of a magnetic moment obtained by a vibrating sample magnetometer. Mossbauer spectroscopy was performed to have an idea about the distribution of ions between the tetrahedral and octahedral sites. Magnetic moment is found to decrease after doping with Ce ions. It was found that the samples show mixed spinel nature rather than the pure inverse character. Doping with Ce ions reduces the EPR linewidth of pure nickel ferrite, which indicates that eddy current losses are reduced.
17 citations
References
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TL;DR: In this paper, the authors report measurements on the ferromagnetic resonance in single-crystal specimens of Co, Ni, and Fe and analyze the linewidth data to obtain the temperature dependence of the Ferromagnetic relaxation frequency, which can be qualitatively understood in terms of recent theories.
Abstract: We report measurements on the ferromagnetic resonance in single-crystal specimens of hcp Co, Ni, and Fe. The linewidth data have been analyzed to obtain the temperature dependence of the ferromagnetic relaxation frequency $\ensuremath{\lambda}$. These temperature dependences can be qualitatively understood in terms of recent theories. On the other hand, it turns out that in some cases $\ensuremath{\lambda}$ is essentially constant over wide ranges of temperature. This behavior is unexplained at present.
194 citations
TL;DR: In this article, a dispersion region is observed in cobalt-zinc ferrites and barium ferrites, and the conductivity of these ferrites is explained by the hopping mechanism.
Abstract: DC conductivity and dielectric studies of CoxZn1−xFe2O4 (x = 0.32, 0.49, 0.79), BaFe12O19, and Mg0.25Zn0.75Fe2O4 are reported as a function of temperature and frequency. The lattice constant and the existence of a single phase are established from X-ray studies. The dielectric behaviour is attributed to the Maxwell-Wagner polarisation. A dispersion region is observed in one of the cobalt-zinc ferrites and the barium ferrite. Activation energies are calculated for these two ferrites from dielectric measurements. The conductivity of these ferrites is explained by the hopping mechanism. Activation energies and the transition temperatures are presented.
Ergebnisse von Gleichstromleitfahigkeits- und dielektrischen Untersuchungen an CoxZn1−xFe2O4 (x = 0,32; 0,49; 0,79) BaFe12O19 und Mg0,25Zn0,75Fe2O4 in Abhangigkeit von der Temperatur und Frequenz werden mitgeteilt. Die Gitterkonstante und die Existenz einer einzelnen Phase werden aus den Rontgenuntersuchungen festgestellt. Das dielektrische Verhalten wird der Maxwell-Wagner-Polarisation zugeschrieben. Ein Dispersionsbereich in einem der Kobalt-Zink-Ferrite und der Barium-Ferrite wird beobachtet. Fur diese beiden Ferrite werden aus den dielektrischen Messungen Aktivierungsenergien berechnet. Die Leitfahigkeit dieser Ferrite wird durch einen Hopping-Mechanismus erklart. Aktivierungsenergien und Ubergangstemperatur werden angegeben.
119 citations
TL;DR: The far-infrared spectra of five mixed ferrites in the range 200 to 640 cm−1 are reported in this article, and four bands are observed. But the spectral properties of these bands are unknown.
Abstract: The far-infrared spectra of five mixed ferrites in the range 200 to 640 cm−1 are reported. Four bands are observed. The high frequency band (v1) and low frequency band (v2) are assigned to the tetrahedral and octahedral complexes, respectively. A small band (v3) around v2 is observed and its intensity increases with divalent octahedral metal ion concentration. This band is assigned to the octahedral divalent metal-oxygen ion complexes. The lowest band observed for the highest concentration of cobalt is attributed to the lattice vibrations of the system.
Die Ferninfrarot-Spektren von funf Mischferriten im Bereich 200 bis 640 cm−1 werden mitgeteilt. Vier Banden werden beobachtet. Die hochfrequente Bande (v1) und die niederfrequente Bande (v2) werden den'tetraedrischen bzw. oktaedrischen Komplexen zugeordnet. Eine schwache Bande (v2) bei v2 wird beobachtet, deren Intensitat mit der Konzentration divalenter oktaedrischer Metallionen zunimmt. Diese Bande wird den oktaedrischen divalenten Metall-Sauerstoff-Komplexen zugeordnet. Die niedrigste Bande, die fur die hochste Kobaltkonzentration beobachtet wird, wird den Gitterschwingungen des Systems zugeschrieben.
95 citations
TL;DR: In this paper, the demagnetization fields arising from the pores between polycrystalline samples are used to explain the dipole narrowing of the linewidth of the anisotropy energy axes from crystallite to crystallite.
Abstract: Two sources of ferromagnetic resonance linewidth in polycrystalline samples which are absent in single‐crystal samples are: (1) the variation in resonant frequencies of the individual crystallites due to the random orientation of the anisotropy energy axes from crystallite to crystallite, and (2) the demagnetization fields arising from the pores between the crystallites. A theory is developed which explains this second contribution to the linewidth in terms of the two‐magnon scattering induced by the demagnetization fields of the pores. Agreement of the theoretical results with experiments is good.The present theory takes into account the dipole narrowing of the linewidth, whereas the previous independent grain theory of Schlomann does not. A second previous theory by Geschwind and Clogston makes an essential mathematical approximation, while the present theory is based on a physical model.
58 citations