Structural and magnetic properties of Bi³⁺ ion doped Ni–Cu–Co nano ferrites prepared by sol–gel auto combustion method

Bismuth doped Ni–Cu–Co nano ferrites with the chemical composition Ni_0.2Cu_0.2Co_0.6Fe_2−xBi_xO₄ (x = 0.0, 0.025, 0.05, 0.075, 0.1) were prepared by sol–gel auto-combustion technology. The analysis of the X-ray diffraction (XRD) patterns confirms that all the samples have a cubic spinel structure. The particle sizes of the prepared samples (between 51 and 55 nm) are determined by the Scherrer equation. The obtained Fourier transform infrared measurement also confirms the formation of the spinel structure. It was observed that with the increase of Bi³⁺ ion concentration, the protruding absorption band was slightly shifted to the high frequency side. Transmission electron microscopy images show the presence of particles which are spherically cubic shaped crystallites. It has been proved that the synthesized ferrite has pure phase and structure by Energy dispersive X-ray, and Bi³⁺-doping was successfully achieved. Cation redistribution in spinel ferrite nanoparticles are confirmed by X-ray photoelectron spectroscopy (XPS). The magnetic parameters of the samples are measured by Vibration sample magnetometer (VSM) at room temperature with a maximum magnetic field of 1 T. It can be clearly observed that the magnetic properties such as saturation magnetization (Ms), remanent magnetization (Mr) and coercivity (Hc) decrease significantly with the bismuth ion concentration increases. This is because Bi³⁺ ions replace Fe³⁺ ions, and Bi³⁺–Fe³⁺ ion interactions are more predominates than Fe²⁺–Fe³⁺ ion interactions. This also indicates that the bismuth doped nickel copper cobalt ferrite has low magnetic properties.