Dielectric, electrical transport and magnetic properties of Er3+ substituted nanocrystalline cobalt ferrite

Erbium substituted cobalt ferrite (CoFe2-xEr5O4; x=0.0-0.2, referred to CFEO) materials were synthesized by sol-gel auto-combustion method. The effect of erbium (Er3+.) substitution on the crystal structure, dielectric, electrical transport and magnetic properties of cobalt ferrite is evaluated. CoFe2-xEr5O4 ceramics exhibit the spinel cubic structure without any impurity phase for x <= 0.10 whereas formation of the ErFeO3 orthoferrite secondary phase was observed for x >= 0.15. All the CFEO samples demonstrate the typical hysteresis (M-H) behavior with a decrease in magnetization as a function of Er content due to weak superexchange interaction. The frequency (f) dependent dielectric constant (epsilon') revealed the usual dielectric dispersion. The epsilon'-f dispersion (f=20 Hz to 1 MHz) fits to the modified Debye's function with more than one ion contributing to the relaxation. The relaxation time and spread factor derived are similar to 10(-4) s and similar to 0.61(+/- 0.04), respectively. Electrical and dielectric studies indicate that epsilon' increases and the dc electrical resistivity decreases as a function of Er content (x <= 0.15). Complex impedance analyses confirm only the grain interior contribution to the conduction process. Temperature dependent electrical transport and room temperature ac conductivity (sigma(ac)) analyses indicate the semiconducting nature and small polaron hopping. (C) 2016 Elsevier Ltd. All rights reserved.