Synthesis, characterization, and magnetic properties of Mn nanoferrites

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.

Enhancement of magnetic losses in hybrid polymer composites with MnZn-ferrite and conductive fillers

Electron spin resonance and cation distribution studies of the Co0.6Zn0.4MnxFe2−xO4 ferrite system

Crystallisation of W-type hexagonal ferrites in an oxide glass with As2O3 as nucleation catalyst

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.

Effect of Ce Doping on the Magnetic Properties of NiFe2O4 Nanoparticles

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.

O. S. Josyulu

Papers

Powder ferromagnetic resonance spectra of some mixed ferrites