Influence of Gd substitution on structural and magnetic properties of Ni0.48Cu0.12 Zn0.40Fe2-x GdxO4

Abstract

Polycrystalline Ni0.48Cu0.12Zn0.40GdxFe2-xO4 (x varies from 0 to 0.10 insteps of 0.02) ferrites were prepared by standard solid state reaction technique. The samples prepared from each composition were sintered at various temperatures in air for 1 hour. Structural and surface morphology were studied by X-ray diffraction and optical microscopy, respectively. The magnetic properties of these ferrites were characterized with high frequency (100Hz-120MHz) complex permeability and temperature dependent permeability measurements. The DC magnetizations as a function of applied magnetic field were measured at room temperature by vibrating sample magnetometer. The effects of microstructure, composition and sintering temperatures on the complex permeability of various Ni0.48Cu0.12Zn0.40GdxFe2-xO4 are discussed. A possible correlation among sintering temperature, grain size and density is also discussed. It was observed that the compositions are single phase and formed spinel structure for small amount of Gd substitution. For x=0.04 sample formed spinel structure with some less intense additional peaks. A gradual increase in the intensity of the additional peaks is noticed with increasing Gd concentration and the peaks are identified to be corresponding to GdFeO3 (orthoferrite phase). The lattice constant of all these samples follow Vegard’s law. The X-ray densities of the samples increase with increasing Gd3+ content. On the other hand, the bulk densities of the samples increases and the corresponding porosity of the samples decreases with increasing of Gd3+ content up to x=0.08. Beyond this value of x, density decreases as well as porosity increases. The sintering densities of the polycrystalline Ni0.48Cu0.12Zn0.40GdxFe2-xO4 increases in increasing sintering temperature up to optimum temperature above that the densities decreases. The microstructural study shows that grain size increases with increasing Gd3+ content up to an optimum concentration after that it decrease. The compositional variation of complex permeability spectra, loss factor and relative quality factor (Q) were studied with frequency for the samples sintered at various temperatures. The general characteristic of the permeability spectra is that the real part of initial permeability ( / μ i ) remain fairly constant in the frequency range up to some critical frequency characterized by the onset of resonance, while at higher frequencies it drops rapidly to a very small value and imaginary part ( // i μ ) increase to have a peak. The Q is found to be increase with increasing Gd3+ content up to an optimum level beyond that it decreases. It is also observed that the Q value decreases with increasing of sintering temperature and loss factors are minimum for frequency up to 1 MHz.The Néel temperature, TN,, of these samples are determined from the temperature dependent initial permeability which shows a decreasing trend as a function of composition due to the weakening of the A-B interaction. Compositional variation saturation magnetization, saturating field, Bohr magneton were calculated from M-H loops measurement. The variation saturation magnetizations were described on the basis of cation distribution.