Embedded ferrihydrite nanoparticles in a SiO2 medium with enhanced superparamagnetic blocking temperature
https://doi.org/10.1016/j.ceramint.2024.11.473
The composite material based on the ferrihydrite nanoparticles (5Fe2O3 · 9H2O) encapsulated in SiO2 matrix was synthesized. Synthesized sample has been characterized by transmission electron microscopy, room-temperature 57Fe Mössbauer spectroscopyand X-ray photoelectron spectroscopy. The data obtained have shown (i) the presence of isolated ferrihydrite nanoparticles with an average size of ∼4.3 nm in the SiO2 matrix and (ii) the complete absence of the nanoparticles binding with the SiO2 matrix. The temperature dependences of the ac and dc magnetization, as well as the temperature evolution of the Mössbauer spectra point out only the occurrence of the superparamagnetic blocking with decreasing temperature. The analysis of the relaxation time of particle magnetic moments have shown no magnetic interactions in the investigated system. A detailed examination of the magnetization curves has revealed that the non-interacted ferrihydrite nanoparticles formed by two magnetic subsystems: paramagnetic surface spins and the magnetically ordered core. Such magnetic morphology results in the significantly decrease of the anisotropy constant (K = 18 ∙ 105 erg/cm3) compared to interacted nanoparticles. At the same time, a decisive role in the magnetic behavior of the material is played by the subsystem of free spins, which involves about half of all iron atoms on the particle surface.