Structural and magnetic studies of the nickel doped CoFe₂O₄ ferrite nanoparticles synthesized by the chemical co-precipitation method

Abstract The physical properties of nickel doped cobalt ferrite nanoparticles Ni_xCo_1-xFe₂O₄ (x=0.5, 0.75, 0.9) derived by the chemical co-precipitation route are characterized by XRD, FTIR, TEM, EPR, search coil and ac susceptibility techniques to develop stable kerosene based ferrofluid. XRD patterns and TEM images confirm the single phase formation of Ni_xCo_1-xFe₂O₄ nanoparticles whose crystallite size increases and lattice parameters decreases with the increase in Ni content. EPR resonance signal peak-to-peak line width and resonance field value decreases with the increase in Ni concentration in these samples. The broad nature of resonance signal is attributed to the ferromagnetic nature of the as-prepared nanoparticles and the increase in super exchange interaction among Ni²⁺-O-Co²⁺ facilitate the shifting of resonance value to lower field. The hysteresis loops of these nickel doped cobalt ferrite analogs exhibits highly magnetic nature of these nanoparticles at ambient temperature whose saturation magnetization, coerecivity and remanence magnetization decreases linearly with the increase in Ni-concentration in cobalt ferrite. The magnetic susceptibility with temperature curve shows increasing trend of blocking temperature with rise in nickel ion concentration.