Magnetic irreversibility and the Verwey transition in nanocrystalline bacterial magnetite

TitleMagnetic irreversibility and the Verwey transition in nanocrystalline bacterial magnetite
Publication TypeJournal Article
Year of Publication2007
AuthorsProzorov R, Prozorov T, Mallapragada SK, Narasimhan B, Williams TJ, Bazylinski DA
Journal TitlePhysical Review B
Volume76
Pages054406
Date PublishedAug
Type of ArticleArticle
ISBN Number1098-0121
Accession NumberISI:000249155100077
KeywordsAMORPHOUS FE2O3, CRYSTALS, FE3O4, MAGNETOTACTIC BACTERIA, MARINE, nanoparticles, PERSPECTIVE, POWDER, relaxation, temperature
Abstract

The magnetic properties of biologically produced magnetite nanocrystals biomineralized by four different magnetotactic bacteria were compared to those of synthetic magnetite nanocrystals and large, high-quality single crystals. The magnetic feature at the Verwey temperature T-V was clearly seen in all nanocrystals, although its sharpness depended on the shape of individual nanoparticles and whether or not the particles were arranged in magnetosome chains. The transition was broader in the individual superparamagnetic nanoparticles for which T-B < T-V, where T-B is the superparamagnetic blocking temperature. For nanocrystals organized in chains, the effective blocking temperature T-B>T-V and the Verwey transition is sharply defined. No correlation between particle size and T-V was found. Furthermore, measurements of M(H,T,time) suggest that magnetosome chains behave as long magnetic dipoles where the local magnetic field is directed along the chain. This result confirms that time-logarithmic magnetic relaxation is due to the collective (dipolar) nature of the barrier for magnetic moment reorientation.

DOI10.1103/PhysRevB.76.054406
Alternate JournalPhys. Rev. B