Articles you may be interested inThermal effect on magnetic parameters of high-coercivity cobalt ferrite J. Appl. Phys. 116, 033901 (2014); 10.1063/1.4890033Structural and ambient/sub-ambient temperature magnetic properties of Er-substituted cobalt-ferrites synthesized by sol-gel assisted auto-combustion method Variations in conductivity with particle size have been observed in cobalt ferrite, when synthesized by solgel auto-combustion method. Impedance analysis reveals metallic and semiconducting behavior at room temperature for a particle size of 6 nm and 52 nm, respectively. Upon thermal activation, metallic to semiconducting phase transition has been observed as a function of particle size and vice-versa. Grainboundary Resistance (R gb ), increased drastically with particle size (19 MX for 6 nm and 259 MX for 52 nm) at room temperature. AC conductivity and dielectric constants exhibit similar metallic to semiconducting phase transition at 6 nm and semiconducting behavior at 52 nm with temperature in the selected frequencies. Enhanced magnetic moment with an increase in the grain size along with decreased coercivity (1444 G to 1146 G) reveals transition from single domain to multi-domain. Increased inter-particle interaction is responsible for metallicity at the nano level and on the contrary semiconductivity is attributed to bulk. V C 2013 AIP Publishing LLC. [http://dx.

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Multiferroic La1-xNaxFeO3 (x = 0.0, 0.05, 0.10, and 0.15) nanoparticles have been synthesized by the citrate sol-gel auto-combustion method. It is uniquely known for the homogeneous distribution of particle size due to the low temperature synthesis condition. The Rietveld refinement of the X-ray diffraction pattern has exhibited the single phase orthorhombic perovskite structure. It is confirmed from micro-Raman analysis that hole doping (Na) produces a structural crossover from the Pnma to Pbnm space group. The red shift observed in UV-visible spectroscopy indicates the shrinkage of bandgap. Photoluminescence analysis supports independently the bandgap shrinkage by the existence of violet-blue emission due to charge disproportion by oxygen related defects. A changeover from semiconductor to metallic nature accompanied by the hopping of charge carriers from Fe3+ to Fe2+/Fe4+ exchange interaction has revealed a considerable increase in conductivity and dielectric constant. Finally, the doping helps to induce transition from an antiferromagnetic to a weak ferromagnetic state due to free carrier concentration. It is found that the hole driven Fe3+ to Fe2+/Fe4+ exchange interactions with change in the Bohr magneton values from 5.9 μB to 4.9/4 μB are responsible for variation in the magnetization values.

Cobalt ferrite nanoparticles have been synthesized by coprecipitation method by varying the precipitation temperatures. The samples have been characterized by x-ray diffraction, impedance analysis, ac conductivity, dielectric, and vibrating sample magnetometer. When the average crystallite size is in the range of 2–16 nm, these compounds behave as metallic, and upon thermal activation, they become semiconducting, indicating anomalous conducting behavior. Impedance analysis reveals a metallic to semiconducting phase transition, accompanied by grain boundary effect, gradually replaced by grain contribution. Ac conductivity measurements and dielectric analysis also confirmed the transformation, when the slope changed from positive to negative as a function of temperature. Particle size independent magnetic behavior was observed in finite size limit due to site exchange of cations between tetrahedral (A) and octahedral (B) sites.

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