Size effects on the magnetic behavior of γ-Fe2O3 core/SiO2 shell nanoparticle assemblies

• Published in: Journal of magnetism and magnetic materials 2021-03, Vol.522, p.167570, Article 167570
• Main Authors: Vasilakaki, Marianna, Gemenetzi, Fevronia, Devlin, Eamonn, Yi, Dong Kee, Riduan, Siti Nurhanna, Lee, Su Seong, Ying, Jackie Y., Papaefthymiou, Georgia C., Trohidou, Kalliopi N.
• Format: Article
• Language: English
• Subjects: Assemblies; Assembly; Blocking temperature; Collinearity; Diameters; Dipolar interparticle interactions; Dipole interactions; Iron oxides; Magnetic cores; Magnetic nanoparticle assemblies; Magnetic properties; Magnetization; Magnetization curves; Monte Carlo simulation; Monte Carlo simulations; Morphology; Nanoparticles; Qualitative analysis; Scale models; Shells; Silicon dioxide; Size effects; Thickness; γ-Fe2O3 core/SiO2 shell morphology
• ISSN: 0304-8853; 1873-4766
• DOI: 10.1016/j.jmmm.2020.167570

•Effect of core size in nano-assemblies of γ-Fe2O3 core/SiO2 shell morphology is investigated.•Thermal stability is enhanced by increasing magnetic core size in these nanocomposites.•For interparticle distance larger than twice the core size, thermal stability decreases rapidly.•Monte Carlo simulations corroborate the important role of dipolar interactions in these assemblies. Theeffect of core size on the magnetic behavior of nanoparticle assemblies of γ-Fe2O3 core/SiO2 shell morphology is investigated. Long-range magnetostatic interactions are probed in two highly monodispersed experimental test systems of spherical nanoparticles with core diameters of 10 nm and 12.5 nm, and a shell thickness varying from 0 nm (bare particles) to ~50 nm. Zero-Field-Cooled magnetization curves are calculated by employing the Monte Carlo simulation technique in a mesoscopic-scale model for the assembly, assuming spin collinearity and coherent spin-reversal mechanisms. Simulation results reproduce the trend in the behavior of the Zero-Field-Cooled magnetization versus T curves in good qualitative agreement with the experimental findings. They also demonstrate that the increase of the magnetic core size results in a shift of the maximum magnetization peak, Tmax, to higher temperatures due to enhanced dipolar coupling. The results shed light on how interparticle distance and magnetic core size influence the value of Tmax through collective behavior and its transition to a single-particle superparamagnetic blocking temperature, TB, as the assembly becomes magnetically diluted with increasing shell thickness.