Magnetic study of different-sized iron oxide nanoparticles

Iron oxide nanoparticles are of great interest in nanomedicine. They are used in Magnetic Resonance Imaging (MRI) as negative contrast agent. In this work, we explored magnetic properties of different-sized magnetite nanoparticles (Fe3O4) by using a Vibrating Sample Magnetometer (VSM). Iron concentration of the solutions was calculated by inductively coupled plasma (ICP) to normalize all measurements.
First, we performed Zero-Field-Cooling (ZFC) and Field-Cooling (FC) curves. Samples were cooled to very low temperature under zero magnetic field (for the ZFC) or under 10 mT (for the FC). At 2 K, the magnetic field was fixed at 10 mT for both curves and magnetization measurements were made in function of the increasing temperature. The average blocking temperature was determined as the maximum of the ZFC [1].
Then, we carried out magnetization measurements in function of the magnetic field at different temperatures. Best Langevin fits [2] to data yielded the average nanoparticles radius and a standard deviation estimation of the lognormal size distribution.
Finally, based on the average blocking temperature and the average radius, we obtained the uniaxial magnetic anisotropy constant KA.

[1] M. Lévy, F. Gazeau, J-C Bacri, C. Wilhelm and M. Devaud, Modeling magnetic nanoparticle dipole-dipole interactions inside living cells, Physical Review B, 84, 075480 (2011)

[2] Y. Gossuin, P. Gillis, A. Hocq, Q. L. Vuong, and A. Roch, Magnetic resonance relaxation properties of superparamagnetic particles, Advanced Review, 1: 299-310 (2009)