Effect of Lanthanum Additive on the Structural, Magnetic, and Morphological Properties of LaxNi1-xFe2O4 Ferrite Prepared by Sol-Gel Method

Spinel ferrites are valued for their tunable electrical and magnetic properties. Rare-earth substitution, such as with La3+, is known to modify their cation distribution and magnetic interaction. In this study, LaxNi1-xFe2O4 nanoparticles (x = 0.0, 0.5, 0.7, and 0.9) were synthesized via the sol-gel method. Their properties were characterized using X-ray diffraction (XRD), vibrating sample magnetometry (VSM), and field-emission scanning electron microscopy (FE-SEM). XRD confirmed a single-phase cubic spinel structure for all compositions. A gradual peak shift with increasing La3+ content indicated lattice expansion, attributable to the larger ionic radius of La3+ compared to Fe3+ and Ni2+. Crystallite size, calculated via the Scherrer equation, also increased with La3+ content. VSM measurement showed typical ferrimagnetic hysteresis loops. Saturation magnetization (Ms) decreased progressively as non-magnetic La3+ ions replaced magnetic Fe3+ and Ni2+ ions, reducing the number of active magnetic sites. This substitution consequently lowered the remnant magnetization (Mr) and coercivity (Hc). FE-SEM images revealed predominantly spherical particles with varying agglomeration, attributed to magnetic and surface forces. The grain size was consistent with XRD estimates. Higher La3+ concentration led to increased agglomeration, reduced shape regularity, and altered particle size distribution and porosity. These results demonstrate that La3+ addition induces significant structural changes, weakens magnetic performance, and alters surface morphology, providing valuable insights for tailoring LaxNi1-xFe2O4 nanoparticles for technological applications.