Experimental characterization of nanocrystalline niobium-doped nickel–zinc ferrites: occurrence of superparamagnetism

• Published in: Journal of materials science Vol. 51; no. 18; pp. 8382 - 8399
• Main Authors: Lakshmi, Ch. S., Sridhar, Ch. S. L. N., Govindraj, G., Bangarraju, S., Potukuchi, D. M.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.09.2016; Springer; Springer Nature B.V
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Classical Mechanics; Coercive force; Coercivity; Core loss; Crystallites; Crystallography and Scattering Methods; Dopants; Electric properties; Ferrites; Grain boundaries; Magnetic saturation; Magnetization; Materials Science; Morphology; Nanocrystals; Nanostructure; Nickel; Niobium; Original Paper; Polymer Sciences; Solid Mechanics; Superparamagnetism; Zinc; Crystallite Size; Ferrite; Nickel Ferrite; Octahedral Site; Ferrite System
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-016-0088-0

Structural, morphological, magnetic, and dielectric investigations are carried out in Nb-doped (viz., for x equal to 0.0–0.4 by wt%) nanocrystalline Ni–Zn ferrites synthesized by hydrothermal method. XRD, IR studies infer the growth of nano structures and Fe 2 O 3 phase. Nb ions segregate at grain boundaries. Crystallite size ( D ) varies from 62 to 18 nm with x . FTIR absorption exhibits split at higher x . Saturation magnetization witnesses an overall decrease with x . Trends of M s ( x ) are explained by nature of dopant, preferential replacement, surface canting ( Y – K angles) and lattice contraction. Variations of coercive field ( H c ) and D infer single-domain to multi-domain morphological transformation. Occurrence of superparamagnetism (SPM) is predicted for zeroed values of H c and for a critical concentration x crit equal to 0.321. Enhanced Nb 5+ –Fe 2+ binding with dopant ( x up to 0.2) results for decrease in dielectric constant ε r ′ , loss factor tanδ and increase in resistivity ρ . Lowered ac conductivity is attributed to blockade of path by Nb 5+ ions in the vicinity of B-sites. Relatively higher ρ (~10 8  Ω cm) and lower loss (tan δ ~10 −2 –10 −3 ) evinced for 10 kHz. Enhanced core loss is realized with x manifested as lowered H c and tan δ to usher their utility in high-frequency applications.