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Spectral and transport phenomena in Ni ferrite-substituted Gd2O3

2001; Elsevier BV; Volume: 224; Issue: 2 Linguagem: Inglês

10.1016/s0304-8853(00)00578-3

1873-4766

O. M. Hemeda, M. Z. Said, M. M. Barakat,

Magneto-Optical Properties and Applications

A series of samples of the system NiGdxFe2−xO4 (x=0, 0.1, 0.3, 0.5 and 0.7) were prepared by the usual ceramic technique. X-ray diffraction, infrared spectroscopy (IR) and electron spin resonance (ESR) have been used to study the mixed ferrite NiGdxFe2−xO4. The X-ray analysis establishes that the samples x=0 and 0.1 have spinel phase structure but x=0.3 and 0.5 samples posses second phase (orthorhombic) besides the spinel one. The main two bands were observed by IR spectra recorded in the range 200–1000 cm−1. The bands at 579 cm−1 (ν1) and 397 cm−1 (ν2) were assigned to tetrahedral (A site) and octahedral (B site) group complexes, respectively. The presence of the bands ν1 and ν11 around ν2 at 307 and 455 cm−1 is the evidence of the entry of Gd3+ ions instead of Fe3+ ions at B site; and these bands appear due to (Gd3+–O2−) stretching vibration. The line width of the ESR spectra decreases with the increased addition of Gd3+ and the ferrite begins to have low electric loss which is very important in application as a core of transformer in microwave region. The DC conductivity was found to increase with increasing temperature. Curie temperature Tc decreases as the nonmagnetic Gd ions increase. NiGd ferrite shows p-type conductivity due to the presence of Ni2+ and Ni3+. The addition of Gd3+ ions creates second orthorhombic phase at x⩾0.3 besides the spinel one. The second intergranual insulating phase increases the resistivity of the samples. The activation energy of conductivity Eσ and that for mobility Eμ show a good agreement which gives evidence for the presence of hopping conduction in the ferrimagnetic region.