Magnetic Behaviour of Nano-Particles of Ni0.8Cu0.2Fe2O4.

Nano-particles of Ni0.8Cu0.2Fe2O4 have been synthesized by the co-precipitation method. Langevin function fitting of the superparamagnetic M– N curve at 290 K provides a log-normal distribution with median diameter of 30 Å and standard deviation of 0.4. Outside a core of ordered spins, moments in the surface layer are disordered. Magnetization evolves over a long period of time t going linearly with log t. Magnetic anisotropy which was estimated by fitting the M–log t curve shows many fold increase over that of bulk particle sample. Major contribution to this enhancement comes form the disordered surface spins. [ABSTRACT FROM AUTHOR]