Magnetic Relaxation of Superparamagnetic Fe Oxide Particles Studied With Mössbauer Spectroscopy

A Mössbauer spectroscopy (MS) study was performed on the superparamagnetic commercially available magnetic fluid, Resovist, with temperatures varying between room temperature and 2.6 K. Two samples were prepared for MS study, one dried specimen and the other frozen. At the lowest temperature of 2.6 K, the spectrum was characteristic of maghemite, and superparamagnetic relaxation was observed with increasing temperature. On the spectrum recorded at 250 K, fitting was performed using the three components in the Blume–Tjon two-state magnetic relaxation model, which resulted in relaxation times of $3.8 \times 10^{-8}$ , $1.7 \times 10^{-8}$ , and $6.4 \times 10^{-10}$ s for the three components.