A recently introduced method for the characterization of magnetic nanoparticles (MNPs) based on the analysis of the temperature-dependent Neel relaxation signal (TMRX) has been applied to characterize maghemite particles with different particle size distributions. The samples were made using an improved magnetic fractionation method for a ferrofluid with a broad particle size distribution. The temperature range of the measurement set-up has been extended from 315 K down to 4 K to detect even the smallest particles in the fractions. A mean magnetically relevant particle size has been derived from TMRX and low temperature coercivity measurements and has been compared to the physical size determined by atomic force microscopy (AFM) investigations.
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