Research Paper

Journal of Nanoparticle Research

, Volume 13, Issue 1, pp 165-173

Investigation of magnetic active core sizes and hydrodynamic diameters of a magnetically fractionated ferrofluid

  • Markus BüttnerAffiliated withInstitute of Solid State Physics, Friedrich Schiller Universität Jena
  • , Peter WeberAffiliated withInstitute of Solid State Physics, Friedrich Schiller Universität Jena
  • , Frank SchmidlAffiliated withInstitute of Solid State Physics, Friedrich Schiller Universität Jena
  • , Paul SeidelAffiliated withInstitute of Solid State Physics, Friedrich Schiller Universität Jena Email author 
  • , Michael RöderAffiliated withINNOVENT e.V.
  • , Matthias SchnabelrauchAffiliated withINNOVENT e.V.
  • , Kerstin WagnerAffiliated withINNOVENT e.V.
  • , Peter GörnertAffiliated withINNOVENT e.V.
  • , Gunnar GlöcklAffiliated withInstitute of Pharmacy, Biopharmaceutics & Pharmaceutical Technology, Ernst-Moritz-Arndt University of Greifswald
    • , Werner WeitschiesAffiliated withInstitute of Pharmacy, Biopharmaceutics & Pharmaceutical Technology, Ernst-Moritz-Arndt University of Greifswald

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Abstract

In this work we address the question which relates between the size of the magnetically active core of magnetic nanoparticles (MNPs) and the size of the overall particle in the solution (the so-called hydrodynamic diameter d hyd) exists. For this purpose we use two methods of examination that can deliver conclusions about the properties of MNP which are not accessible with normal microscopy. On the one hand, we use temperature dependent magnetorelaxation (TMRX) method, which enables direct access to the energy barrier distribution and by using additional hysteresis loop measurements can provide details about the size of the magnetically active cores. On the other hand, to determine the size of the overall particle in the solution, we use the magnetooptical relaxation of ferrofluids (MORFF) method, where the stimulation is done magnetically while the reading of the relaxation signal, however, is done optically. As a basis for the examinations in this work we use a ferrofluid that was developed for medicinal purposes and which has been fractioned magnetically to obtain differently sized fractions of MNPs. The two values obtained through these methods for each fraction shows the success in fractioning the original solution. Therefore, one can conclude a direct correlation between the size of the magnetically active core and the size of the complete particle in the solution from the experimental results. To calculate the size of the magnetically active core we found a temperature dependent anisotropy constant which was taken into account for the calculations. Furthermore, we found relaxation signals at 18 K for all fractions in these TMRX measurements, which have their origin in other magnetic effects than the Néel relaxation.

Keywords

Magnetic nanoparticles Temperature dependent magnetorelaxation Magnetooptical relaxation Anisotropy Hydrodynamic size Magnetite Maghemite Core size Colloids