(a) TEM images of concentrated zero-field-dried and [(b) and (c)] concentrated field-dried ferrofluids.
(a) Temperature dependence of magnetization under ZFC and FC conditions measured in for the diluted-ZFF, diluted-FF, concentrated-ZFF, and concentrated-FF samples. (b) The positions of the in ZFC susceptibility for all four samples are indicated by arrows. The inset shows a magnification of the curve for the concentrated-FF sample around the peak.
Temperature dependence of the in-phase component of the ac susceptibility for the diluted-ZFF sample measured in a magnetic field of amplitude 6.5 Oe at frequencies of 1, 10, 100, and 1000 Hz.
The logarithm of the inverse value of measuring frequency vs the inverse value of the blocking temperature for the diluted-ZFF and the diluted-FF samples. The measured data are fitted by the Arrhenius law [Eq. (1)].
The inverse value of measuring frequency vs blocking temperature for the concentrated-ZFF sample and the concentrated-FF sample. The measured data are fitted with the Vogel–Fulcher law [Eq. (2)].
(a) Field dependence of magnetization per unit mass of magnetic particles for the diluted-ZFF, diluted-FF, concentrated-ZFF, and concentrated-FF samples. (b) Low field behavior for the concentrated samples.
The anisotropy energy and the particle diameters (, ) obtained from ac susceptibility and measurements.
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