Impact of La3+ doping on the structural, magnetic, and dielectric properties of Mg–Co ferrites for high-frequency applications

Abstract

In this study, the influence of La³⁺ ion doping on the microstructure, crystallite size, as well as magnetic and dielectric properties of Mg_0.5Co_0.5Fe_2−xLa_xO₄ (0 ≤ x ≤ 0.1) ferrite nanoparticles is examined. The La³⁺ ion has a larger ionic radius than the Fe³⁺ ion and occupies the octahedral site, resulting in the expansion of the crystal lattice. Thus, it is expected that replacing La³⁺ ions with Fe³⁺ ions could enhance the electrical and magnetic properties of spinel ferrites, making them suitable for various applications. Mg_0.5Co_0.5Fe_2−xLa_xO₄ nanoparticles were synthesized using the co-precipitation method. X-Ray diffraction analysis confirms the cubic phase structure of all samples, further supported by characteristic peaks obtained from Fourier-transform infrared spectroscopy. The crystallite size ranged from 6 nm to 14 nm, with the lattice parameter increasing from 8.367 Å to 8.379 Å as La³⁺ ion doping increased. High-resolution transmission electron microscopy revealed that the nanoparticles possessed a spherical shape with agglomeration. Magnetic hysteresis analysis indicated that the saturation magnetization of the Mg–Co ferrite nanoparticles decreased from 35.79 emu g⁻¹ to 27.12 emu g⁻¹ with increasing La³⁺ ion concentration. Vibrating sample magnetometry confirmed the superparamagnetic behavior of the synthesized nanoparticles. Electron spin resonance spectroscopy demonstrated a reduction in the g-value from 5.84 to 3.42 and spin relaxation time with increasing La³⁺ doping. These magnetic characteristics suggest that the nanoparticles are promising candidates for ferrofluid synthesis and biomedical applications. Dielectric studies demonstrated a distinct reduction in the dielectric constant (ε′) and loss tangent (tan δ) with increasing La³⁺ content, which optimizes these nanoparticles for advanced microwave and RF applications. These findings establish a direct link between La³⁺ doping and enhanced functional properties, offering novel insights into designing ferrite-based materials for emerging technologies.