Study on the mechanism of tunable ferromagnetic composites with different rare earth ions

Size-controlled Fe₃O₄ nanoparticles doped with rare earth (RE) ions (La³⁺, Ce³⁺, and Dy³⁺) varying from 15 nm to 30 nm were successful synthesized by a hydrothermal method for potential applications in the fields of biomedicine, environmental protection and magnetic memory devices. They possessed good dispersibility, adjustable particle size and nearly spherical shape. The particle grain size was uniformly distributed and showed a low degree of agglomeration in comparison with undoped Fe₃O₄ nanoparticles. The FTIR results showed that the RE elements partially replaced Fe²⁺, occupied the octahedral position, and enhanced the vibration of the Fe-O bond. The XPS study further revealed that the valence states of La, Ce, and Dy are both positive trivalent. The XPS Fe 2p valence band spectra observed a shift in the peak position toward higher binding energy after RE doping, confirming the existence of RE ions in the octahedral position. This paper explains the mechanism of rare earth doping with Fe₃O₄, and clarifies the influence of the doping of different RE ions on its magnetic properties. The detailed analysis of RE-doped ferrite materials can open a new perspective in designing biomedical and spintronics materials with tailored properties by choosing suitable cation substitution.