The magnetization reversal of chains of 40-50 nanometer, magnetic particles has been studied using Magnetic Force Microscopy (MFM) in an applied field. The field was stepwise increased and decreased in order to make hysteresis loops for the chains. The magnetic particles, magnetosomes biomineralized by magnetotactic bacteria, are single crystal Fe3O4 with a narrow size distribution. A method for extracting Switching Field Distributions (SFD's) from sets of MFM images of such chains was developed. The coercivity was found to increase with the number of particles in a chain up to 7 or 8 particles and then decrease with increasing number of magnetosomes. After the initial reversal observations, one of the chains was cut into smaller pieces using the MFM-tip, thus producing separated chain segments, which resulted in altered inter-particle interactions. Additionally, multiple hysteresis loops were made for the same chain, showing that the field from the tip affects the sample magnetization.
|Original language||English (US)|
|Number of pages||4|
|State||Published - 1999|
|Event||Proceedings of the 1998 4th International Conference on Nanostructured Materials (NANO '98) - Stockholm, Swed|
Duration: Jun 14 1998 → Jun 19 1998
Bibliographical noteFunding Information:
In conclusion,w e have measuredth e coercivef ield of three isolatedc hains of octahedraslh apedm agnetitep articlesw ith an approximatesi ze of 40-50 nm producedb y magnetotactbica cteriaW. e showt hati t is possiblet o calculateS witchingF ield Distributions (SFD’s) for serieso f imageso btainedb y MagneticF orce Microscopy of single magnetic domainp articles.W e find the chain segmentso f magnetosomeasp peart o reverset heir magnp.tizatiionn a mannecr onsistenwt itht hec haino f spherefsa nningm odelf or up to 7 or 8 particlesw, itha decreasien thec oercivityf or longerc hainsI.t mayb e for theselo ngerc hainsa morec ollectiver eversaml echanisma,k into a domainw all,d ominates. This researchw as supportedb y the Swedish National Board for Technical and IndustriaDl evelopmentN, UTEK and the U.S. Office of Naval ResearchO. ne of us (JW) acknowledgetrsa velg rantsf rom the Royal Instituteo f Technologya ndThe Royal Swedish Academyo f Sciencesw, hich madep ossiblev isits to the MagneticM icroscopyC entera t the Universityo f Minnesotafo r carryingo uta parto f thisw ork.