Erbium (Er 3+ ) substituted nanocrystalline, cobalt-rich ferrites, which can be represented chemically as Co 1.1 Fe 1.9−x Er x O 4 (CFEO; x = 0.0−0.2), were synthesized by the sol−gel autocombustion method. The structural, dielectric, and electrical transport properties of CFEO were investigated in detail. CFEO materials crystallize in a spinel cubic structure for x ≤ 0.10; formation of orthoferrite (ErFeO 3 ) secondary phase was noted for x ≥ 0.15. Microstructural and compositional studies revealed the formation of spherical, elongated grains with stoichiometric presence of Co, Fe, Er, and O. The dielectric constant (ε′) dispersion fits to the Debye's function for all CFEO ceramics. The relaxation time and spread factor obtained from ε′ dispersion are ∼10 −3 s and ∼0.50 (±0.10), respectively. The complex impedance analyses confirm a graininterior mechanism contributing to the dielectric properties. Semiconducting behavior and small polaron conduction mechanism were evident in electrical transport properties of CFEO materials.

Erbium substituted cobalt ferrite (CoFe 2−x Er x O 4 ; =0.0-0.2, referred to CFEO) materials were synthesized by sol-gel auto-combustion method. The effect of erbium (Er 3+) substitution on the crystal structure, dielectric, electrical transport and magnetic properties of cobalt ferrite is evaluated. CoFe 2−x Er x O 4 ceramics exhibit the spinel cubic structure without any impurity phase for x0.10 whereas formation of the ErFeO 3 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 (ε′) revealed the usual dielectric dispersion. The ε′-f dispersion (f=20Hz-1MHz) fits to the modified Debye's function with more than one ion contributing to the relaxation. The relaxation time and spread factor derived are 10-4 s and 0.61(0.04), respectively. Electrical and dielectric studies indicate that ε′ 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 (σ ac) analyses indicate the semiconducting nature and small polaron hopping.

Induced strain and magnetostrictive coefficient (λ11) with the applied magnetic field (H) for different compositions of Co1.1Fe1.9−xErxO4.

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