The effect of particle size on structural and magnetic properties of Sm3+ ion substituted Zn-Mn nanoferrites synthesized by glycol-thermal method

Abstract

Zn0.5Mn0.5SmxFe2-xO4 (0 ≤ x 0.05) fine powders with average crystallite sizes in the range 12–17 nm were synthesized by glycol-thermal reaction. The as-prepared compounds were subjected to thermal annealing process at 1100 °C, after which the crystallite sizes increased to about 60 nm. XRD analysis confirmed a single-phase cubic spinel structure in all the compounds investigated. TEM images showed nearly spherical particles with uniform particle size distributions. SEM and FTIR have been used to study morphology and confirm phase formation, respectively. The Mössbauer spectrum for Zn0.5Mn0.5Fe2O4 (x = 0) at room temperature may be resolved into two quadrupole doublets indicative of paramagnetic spin state. Sm3+ substituted compounds showed weak sextets in addition to broad doublets attributed to some particle magnetic moments in ordered magnetic phase. The Mössbauer spectra of the compounds annealed at 1100 °C exhibit magnetic split sextets indicative of ordered magnetic phase. The compounds have small coercive fields and high saturation magnetization (40 emu/g to 60 emu/g) which reduce with increasing Sm3+ content due to the paramagnetic nature of Sm3+ ions. Magnetic measurements as a function of field and temperature in as-prepared particles showed superparamagnetic behaviour with average moment of about ≈104μB. The average particle size obtained from the magnetic data corresponds well with that estimated from XRD analysis.