Effect of Nickel Ferrite on Electrical and Magnetic Properties in LCMO: Nickel Ferrite Nanocomposites

Composites of (1-x)M LCMO: xM NiFe₂O₄ (where M is molecular weight and x = 0, 0.01, 0.02, 0.05, 0.10, 0.15, 0.50 and 1) were prepared by precipitation route using microwave oven and sintered at 1200 °C to understand the effect of NiFe₂O₄ addition on the structure, transport and magnetic properties of La-Ca-manganite. A structural transition from monoclinic LCMO (x ≤ 0.10 M, space group I 2/a) to orthorhombic LCMO ( x ≥ 0.15 M, space group P n m a) was observed with increasing NiFe₂O₄ concentration. The presence of two insulator-metal (T_MI) transition at 245 and 210 K for x = 0, and at 245 K and 165 K for x = 0.01 M composite in ρ versus temperature curve was due to the intergrain scattering and presence of microscopic inhomogeneities, respectively. The T_MI suppressed to 87 K for x = 0.02 M, while composites with NiFe₂O₄ ≥ 0.05 M, do not show any transition and exhibit a semiconducting/insulating behavior. Magnetoresistance (MR) was found to be nearly 18% at T_MI for x = 0 and x = 0.01 M composite. The Curie temperature (T_c) of LCMO decreases from 240 to 120 K with NiFe₂O₄ addition up to x = 0.15 M. There was a transition from hard (0.05 M ≤ x ≤ 0.15 M) to soft ( x >; 0.15 M) ferromagnetic behavior with increasing NiFe₂O₄ concentration. Magnetic coercivity (H_c) as high as 640 Oe was obtained in 0.85 M LCMO: 0.15 M NiFe₂O₄ composite.