Synthesis and characterization of low temperature superparamagnetic cobalt ferrite nanoparticles

Department of Applied Physics, Visvesvararya National Institute of Technology, Nagpur 440010, India

Adv. Mater. Lett., 2017, 8 (4), pp 435-443

DOI: 10.5185/amlett.2017.6900

Publication Date (Web): Mar 14, 2017

Copyright © IAAM-VBRI Press

E-mail: k.mohankant@gmail.com

Abstract

Cobalt ferrite (CoFe₂O₄) nanoparticles were synthesized by co-precipitation route at 80 °C. X-ray diffraction pattern (XRD) confirmed cubic inverse spinel structure of CoFe₂O₄ nanoparticles. The average crystallite size of CoFe₂O₄ nanoparticles estimated by X-ray line profile fitting was 12±2 nm for high-intensity peak (311). The particle size, distribution and surface morphology was estimated using Transmission electron microscopy (TEM) with average particle size of 16±2 nm. Raman spectra of CoFe₂O₄ nanoparticles exhibits phonon modes corresponding to tetrahedral sites (679 cm^-1) and octahedral sites (465 cm^-1) respectively. The saturation magnetization Ms for CoFe₂O₄ sample is found to be 63 and 82 emu/g at 300 K and 10 K respectively. The cubic magnetic anisotropy constant K₁ and saturation magnetization M_s are obtained by fitting M versus H isotherm to the saturation approach law. By fitting, K₁ and M_s is 2.16 x10⁵ J/m³ and 66 emu/g respectively at 300 K. The cubic magnetic anisotropy constant K₁ = 5.49 x10⁵ J/m³ is evaluated at blocking temperature of 144 K. The particle size and L-S coupling is responsible for superparamagnetic behaviour of CoFe₂O₄ nanoparticles. Fitting of FC curve provides Curie temperature at T_c = 823K using modified Bloch’s law for CoFe₂O₄ nanoparticles. Tunable particle sizes by controlling the magnetic anisotropy and L-S coupling will tailor magnetic properties and usage in bio-medical applications

Keywords

CoFe₂O_4,co-precipitation, L - S coupling, superparamagnetism, anisotropic constant.