Microstructure mediated weak ferromagnetism in La-doped CeO₂ nanoparticles

Magnetism in La-doped CeO₂nanoparticles depends on doping percentage, ordering length, cation-vacancy exchange interaction, cationic segregation at the surface and other factors. This work explores microstructure and low-temperature magnetic property of 4% La-doped CeO₂ nanoparticles. Nanoparticles are synthesized by a simple solvothermal method followed by sintering at 550 °C. Microstructural analysis by Rietveld refinement of X-ray diffraction pattern reveals that the compound crystallizes in a face-centered cubic fluorite structure with lattice parameter 5.4326 Å. The calculated crystallite size by Rietveld refinement is ~ 9.4 nm. About 5% oxygen vacancy is created in the compound due to aliovalent doping of Ce⁺⁴ cations by La⁺³ cations. The microstructure of the compound is also confirmed from HRTEM images. The average diameter of well-dispersed spherical nanoparticles is measured as ~ 8–9 nm. The crystal structure of the compound is also verified with the SAED pattern. The EDX spectrum confirms the presence of La dopant along with Ce and O in the compound. The band gap of the compound calculated from the UV–VIS absorption spectrum is ~ 2.81 eV. The 4% La-doped CeO₂ dispersed nanoparticles exhibit a weak low-temperature ferromagnetic behaviour. The bifurcation between ZFC and FC is found up to 150 K from M-T measurements. Small hysteresis loops are found at all measuring temperatures. At 50 K, the coercive magnetic field is 232 Oe with remnant magnetization of 0.52 × 10^–6 emu/g and saturation magnetization of 1.9 × 10^–6 emu/g. Weak ferromagnetism is observed in the nanoparticles as cation-vacancy ferromagnetic interaction is limited by ordering length and dopant segregation on the surface of the compound.