Magnetic behaviour of nano-particles of Ni_0.5Co_0.5Fe₂O₄ prepared using two different routes

366-370Literature reports on bulk sample of the ferrite Ni0.5Co0.5Fe2O4 confirm a complete inverse spinel structure. On site occupancy and magnetic anisotropy on nano-particle samples of the titled ferrite prepared using two different routes – a wet chemical co-precipitation process and sol-gel method have been studied. Estimated average particle sizes of the two samples (referred to as NCWET and NCSOL) are ~75Å and ~190Å respectively. Small angle neutron scattering measurements made on the fluid sample comprising the sample prepared by wet chemical process gives median size ~77Å with standard deviation σ = 0.60. Mössbauer studies at 300K show that the two ferrite samples maintain inverse spinel structure even in nano-crystalline state. Magnetization and Mössbauer measurements show that part of the sample in both the cases is in superparamagnetic state. Magnetic anisotropy is larger in the nano-particle state and surface spin disorder also contributes to this