Synthesis and size dependent magnetic behaviour of nanocrystalline Cu[sub 0.2]Ni[sub 0.8]Fe[sub 2]O[sub 4] ferrite

Particle size has significant effect on the magnetic properties of nano‐particles. Nano‐particles of Cu‐Ni ferrite have been synthesized by the co‐precipitation method. Different particle sizes (3nm‐9 nm) were obtained by annealing the prepared samples at various temperatures. The specimens characterized using XRD confirmed the formation of cubic spinel structure. The samples show typical superparamagnetic behaviour above blocking temperature. The particle size increases with increasing the annealing temperature. The saturation magnetization & blocking temperature increases with particle size which is characteristic of superparamagnetism. The hysteresis curves show reduction in saturation magnetization in the case of nanoparticles as compared to their bulk counterpart, which have been explained on the basis that the magnetic moments in the surface layers of a nanoparticle are in a state of frozen disorder. However the saturation magnetization increases with particle size, which is the characteristic property of single domain superparamagnetic particles.