Magnetic properties of bacterial magnetosomes and chemosynthesized magnetite nanoparticles

M. Timko¹ - A. Dżarová¹ - V. Závišová¹ - M. Koneracká¹ - A. Šprincová^{1, 4} - P. Kopċanský¹ - J. Kováċ¹ - I. Vávra² - A. Szlaferek³

¹ Institute of Experimental Physics SAS, Watsonova 47, 040 01 Košice, Slovakia
² Institute of Electrical Engineering SAS Dúbravská 9, 841 04 Bratislava, Slovakia
³ Institute of Molecular Physics PAN, Smoluchowskiego 17, 60-179 Poznan, Poland
⁴ Laboratory of Radiation Biology, Joint Institute for Nuclear Research, Dubna, Russia

Abstract
In this work, the magnetic properties of biologically produced magnetite (magnetosomes) by a mineralization process of magnetotactic bacteria Magnetospirillum sp. AMB-1 were compared to those of chemically synthesized magnetite nanoparticles and nanorods. X-ray diffraction data reveal that for all samples the peaks come from magnetite. A sharp magnetic transition (Verwey transition) is clearly observed in magnetosomes at 105 K (magnetite nanocrystals obtained by mineralization) and nanorodes at 112 K, in opposite, this transition is significantly smeared in Fe₃O₄ powder, where the magnetic nanoparticles are separated and the magnetic fluctuations are strong to overcome magnetic anisotropy and randomize magnetic moment. The existence of coercivity of 71 Oe at room temperature is related to the fact that the mean diameter (34 nm) is larger than the critical size for the transition from superparamagnetic to ferromagnetic behaviour. Figs 6, Refs 14.