Monitoring the evolution of Fe3O4 mesocrystal morphology using first-order reversal curves

• Published in: Journal of magnetism and magnetic materials 2021-04, Vol.524, p.167656, Article 167656
• Main Authors: Kobayashi, Satoru, Yamaya, Sachiko
• Format: Article
• Language: English
• Subjects: Coercivity; Crystallography; Evolution; First-order reversal curves; Iron oxides; Magnetic hysteresis; Magnetite; Mesocrystal; Monitoring; Morphology; Nanoparticle; Nanoparticles; Reaction time
• ISSN: 0304-8853; 1873-4766
• DOI: 10.1016/j.jmmm.2020.167656

•First-order reversal curves (FORCs) are measured for magnetite mesocrystals comprising small nanoparticles with nearly identical crystallographic orientations.•As the reaction time increases, both switching field and local interaction field increase with the development of the particle size, suggesting that the magnetic hardening and increased magnetostatic interactions between small nanoparticles.•At a large reaction time, the mesocrystal splits into porous nanoparticles with higher coercivity. We report the results of systematic measurements of first-order reversal curves (FORCs) for magnetite (Fe3O4) mesocrystals during the reaction process, where small nanoparticles, all with the same crystallographic orientation, form a cluster, and as the reaction time increases, grow in size. The FORC distribution exhibits a single peak in the FORC diagram, whose position gradually shifts toward a higher coercivity as the reaction time increases, which is associated with the broadening of the peak along both the coercivity and local interaction field axes. In addition, the FORC distribution peak is slightly displaced toward a negative local interaction field. These observations suggest the magnetic hardening and the presence of a positive (magnetizing) mean field acting on an individual nanoparticle from the surrounding nanoparticles within a mesocrystal. As the reaction time is further increased, nanoparticles constituting a mesocrystal split into porous nanoparticles, which is associated with a further shift of the FORC peak toward a higher coercivity. The present study demonstrates that FORCs can be a powerful tool for monitoring the morphology evolution of magnetic mesocrystals composed of small nanoparticles.