Temperature dependent magnetic properties of superparamagnetic CoFe2O4 nanoparticles.

Cobalt ferrite (CoFe 2 O 4) nanoparticles were prepared by chemical co-precipitation route at low temperature (70 °C). X-ray diffraction pattern confirms the cubic inverse spinel structure with an average crystallite size of ∼14 nm. Transmission electron microscopy exhibits a narrow distribution of particle size with an average particle size of 15 nm. The synthesized nanoparticles exhibited a saturation magnetization of 23.2 e m u / g and 33.6 e m u / g at 300 K and 20 K respectively. The randomly oriented spin layer thickness of 1.74 nm calculated at room temperature reduces the value of magnetization in as-synthesized nanoparticles. Exponential decay was observed in coercivity (H c) and remanence magnetization (M r) with the increase in temperature from 20 K to 300 K. Blocking temperature of 250 K is found from d (Z F C − F C) d t versus T curve. The plot of H H T versus T revealed the superparamagnetic behavior and exhibited largest superparamagnetic moment at 300 K. The effective anisotropy constant and surface anisotropy constant were calculated to be 6.00 × 104 J/m3 and 1.08 × 10−4 J/m2 respectively at blocking temperature. • Reduction in M s values with increasing temperature is attributed to the presence of non- magnetic surface layer and spin canting. • As synthesized single domain magnetic nanoparticles exhibited large magnetic moment per particle. • Dependence of superparamagnetic moment ((μ s p)) with temperature (T) and applied magnetic field (H) has been analysed systematically. • From vs. T graph, temperature ranges were measured for which as synthesized CoFe2O4 exhibits superparamagnetic behavior. • At 250 K and 300 K as synthesized CoFe2O4 nanoparticle exhibits superparamagnetic behavior with highest superparamagnetic moment 1.54 × 104 μB at T = 300 K. • The magnetic properties of cobalt ferrite nanoparticles synthesized in present work can be used as base ferrite materials environmental and biomedical applications. [ABSTRACT FROM AUTHOR]