Electric, dielectric and magnetic characteristics of Cr~(3+), Mn~(3+) and Fe~(3+) substituted MgAl_2O_4: Effect of pH and annealing temperature

摘要

MgAl_2O_4 spinel and its doped derivatives with transition metals (Cr~(3+), Mn~(3+) and Fe~(3+)) have been synthesized at different pH values by the chemical coprecipitation method in the range 5-10. Powder X-ray diffraction of the samples indicates that a single phase spinel is synthesized at pH >= 5. The average Scher-rer crystallite sizes of the synthesized samples are in the range of 5-15 nm. The endothermic peaks in differential thermal analysis show that the coprecipitate is initially formed at 150 deg C that decomposes to form the spinel phase at 240-270 deg C The quantitative elemental analysis by energy dispersive X-ray florescence shows that the samples are nearly stoichiometric. Surface morphology studied with the help of scanning electron microscopy and scanning probe microscopy reveals the existence of both the individual nanoparticles and their aggregates. The dc electrical resistivity is measured by the two-point probe method in a temperature range of 25-400 deg C. The electrical resistivity, dielectric constant and dielectric loss of MgAl_2O_4 are enhanced by the substitution of Cr~(3+), Mn~(3+) and Fe~(3+). Iron doped samples are found to be paramagnetic while the rest are diamagnetic in nature.