Effect of particle size on the magnetic properties of NixCo1−xFe2O4 (x ≈ 0.3) nanoparticles

NixCo1−xFe2O4 (x ≈ 0.3) nanoparticles were synthesized via chemical co-precipitation method. The particle size (d) was found to increase linearly with increasing annealing temperature. Magnetic studies revealed that the coercivity (HC) attains a value of 965 Oe at ∼18 nm and then decreases for larger particles. The behavior of HC with d was attributed to the superparamagnetic nature of smaller nanoparticles, whereas for larger particles it was attributed to domain transformation mechanism. Both saturation magnetization (MS) and superparamagnetic blocking temperature (Tb) were found to increase linearly with increasing size of the nanoparticles.