title: Interparticle interactions in agglomerates of alpha-Fe2O3 nanoparticles: influence of grinding.
abstract: We have chemically prepared a sample of antiferromagnetic alpha-Fe2O3 nanoparticles by a gel-sol technique. Mössbauer spectra of the as-prepared sample showed that superparamagnetic relaxation was suppressed due to strong magnetic interparticle interactions even at room temperature. However, subsequent grinding of the sample by hand in a mortar for some minutes resulted in fast superparamagnetic relaxation of some of the particles. The effect was even more dramatic if the alpha-Fe2O3 powder was ground for a longer time or together with nonmagnetic eta-Al2O3 nanoparticles. Similar effects were found after low-energy ball milling. Thus it is found that the agglomeration of the nanoparticles during preparation under wet conditions results in strong magnetic interparticle interaction, but a relatively gentle mechanical treatment is sufficient to break up the agglomerates, resulting in much weaker interactions. We show that these effects can also be seen when a soil sample containing magnetic nanoparticles is ground.
authors.affiliation: Department of Physics, Bldg. 307, Technical University of Denmark, DK-2800 Kgs. Lyngby.
authors.forename: Min
authors.initials: M
authors.lastname: Xu
authors.forename: Christian R H
authors.initials: CR
authors.lastname: Bahl
authors.forename: Cathrine
authors.initials: C
authors.lastname: Frandsen
authors.forename: Steen
authors.initials: S
authors.lastname: Mørup