COMPLEX PERMEABILITY AND POWER LOSS MEASUREMENTS ON Ni-Zn-In-Ti FERRITES

Polycrystalline high saturation magnetization nickel-zinc ferrites with fixed quantity of indium and varied quantities of titanium and zinc with the general formula Ni0.65Zn0.35+xIn0.01TixFe1.99-2x O4, where x varies from 0.00 to 0.25 in steps of 0.05, have been prepared by conventional ceramic technique to examine their usefulness for high frequency power applications. Sintering of the samples was carried out at 1250 °C for 4 hours in air atmosphere followed by natural cooling. X-ray diffraction patterns confirm single phase spinel structure in all the samples. Complex permeability measurements exhibit a stable frequency response up to 5 MHz beyond which the real permeability drops and imaginary permeability increases to display a peak around 10 MHz. Power loss density has been observed to be very low up to 3 MHz, however, it increases rapidly beyond 3 MHz; thus it is suggested that these materials could be useful as core materials up to 3 MHz. The results are analysed and discussed in terms of the changes in compositions, microstructure and the associated processes of resonance and relaxation due to domain wall movements and damping of spin rotations contributing to the variations in permeability and losses

Physical characteristics and cation distribution of NiFe2O4 thin films prepared by reactive co-sputtering

Klewe C, Meinert M, Böhnke A, et al. Physical characteristics and cation distribution of NiFe2O4 thin films prepared by reactive co-sputtering. Journal of Applied Physics. 2014;115(12): 123903.We fabricated NiFe2O4 thin films on MgAl2O4 (001) substrates by reactive dc magnetron co-sputtering in a pure oxygen atmosphere at different substrate temperatures. The film properties were investigated by various techniques with a focus on their structure, surface topography, magnetic characteristics, and transport properties. Structural analysis revealed a good crystallization with epitaxial growth and low roughness and a similar quality as in films grown by pulsed laser deposition. Electrical conductivity measurements showed high room temperature resistivity (12Xm), but low activation energy, indicating an extrinsic transport mechanism. A band gap of about 1.55 eV was found by optical spectroscopy. Detailed x-ray spectroscopy studies confirmed the samples to be ferrimagnetic with fully compensated Fe moments. By comparison with multiplet calculations of the spectra, we found that the cation valencies are to a large extent Ni2+ and Fe3+