Room temperature Mössbauer spectra for Fe₃O₄ nanoparticles (a) bare, dry milled for 7.5 hrs, 15.3 nm diameter and ((b)–(d)) wet milled in hexane for 6 hrs with various percent amounts of oleic acid by mass to hexane, (b) 5% OA, 10.7 nm, (c) 10% OA, 9.4 nm, (d) 20% OA, 8.0 nm diameter. The solid line through the experimental points is the least-square fit of the experimental data to a superposition of magnetic slow relaxation (turquoise and blue), superparamagnetic fast relaxation (red), and intermediate relaxation (green) spectral signatures indicated above the spectra (see text and Table 3).