Study of lanthanum ions (La${}^{3+}$) doped Manganese-Cobalt (Mn-Co) based spinel ferrite nanoparticles for technological applications

Nowadays, spinel ferrites are the subject of research as their structural, magnetic, and dielectric properties are quite prominent for applications in the magnetic and electrical fields. In this work, nanoparticles of manganese-cobalt spinel ferrite (Mn${}_{0.7}$Co${}_{0.3}$La${}_x$Fe${}_{2-x}$O${}_4$), with 0-10% doping variation of lanthanum ions, are prepared by Sol-Gel auto-combustion route. The powder obtained from the synthesis was annealed in a muffle furnace at 600 °C for 4 h. XRD results confirmed the formation of the face-centered cubic (FCC) structure with a space group of Fd3m in La${}^{3+}$ doped Mn-Co based spinel ferrites. The crystallite size was calculated from the Scherrer formula, found in the 9-14 nm range. Surface morphology was performed using SEM, revealing that non-uniform spherical shape grains with agglomeration are observed with the La${}^{3+}$ ions doping. FTIR transmittance versus wave number pattern represents two absorption bands corresponding to tetrahedral and octahedral sites. The electrical properties are investigated in the 1 MHz to 3 GHz frequency range, and obtained results are described using the Maxwell-Wagner model. A decreasing trend in the impedance and dielectric constant is observed with the increasing applied frequency for all concentrations of La. The highest impedance value is found for the sample with La concentration x = 0.15. Electric modulus Cole-Cole plots showed grain and grain boundary contribution to the conduction process. The hysteresis loop from VSM data confirms that the prepared ferrites are soft magnetic materials. The increasing concentration of La${}^{3+}$ ions significantly declines the coercive field and remanent magnetization. According to the findings, the prepared ferrite materials are appropriate for microwave and charge storage applications. On the other hand, La-doped Mn-Co ferrites are an excellent choice for soft magnetic applications such as transformer cores and magnetic storage devices.