Magnetic behaviour of nanocrystalline Ni–Cu ferrite and the effect of irradiation by 100 MeV Ni ions

The effects of 100 MeV Ni ion irradiation on magnetic properties of nanoparticles of Ni_0.8Cu_0.2Fe₂O₄ with average particle sizes of 40 Å and 60 Å, synthesized by chemical co-precipitation method have been studied. The spinel cubic structures were confirmed by XRD. The average particle size estimated by XRD and by Langevin function fitting are in good agreement for both the pristine and irradiated samples. The blocking temperature increases with particle size and does not change after irradiation. On irradiation by 100 MeV Ni ions, significant changes in the hysteresis loop features are observed, which may be attributed to formation of cluster of defects in the nanocrystalline samples due to swift heavy ion (SHI) irradiation. It is also found that SHI irradiation produces more dominant changes in the hysteresis loop of smaller particle size of 40 Å as compared to that of 60 Å.