Spectral and transport phenomena in Ni ferrite-substituted Gd2O3

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 = O 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 200-1000cm(-1). The bands at 579 cm(-1) (v(1)) and 397cm(-1) (v(2)) were assigned to tetrahedral (A site) and octahedral (B site) group complexes, respectively. The presence of the bands vl and v(11) around v(2) 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 T-c 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 greater than or equal to 0.3 besides the spinel one. The second intergranual insulating phase increases the resistivity of the samples. The activation energy of conductivity E-sigma and that for mobility E-mu show a good agreement which gives evidence for the presence of hopping conduction in the ferrimagnetic region. (C) 2001 Elsevier Science B.V. All rights reserved.